Introduced in 1988, General Motors’ GMT 400 truck platform and its various permutations represented a significant technological step forward from the C/K series architecture that preceded it, the latter of which could trace its origins all the way back to the late 1950s. Now colloquially known as Old Body Style (OBS) pickups, these trucks and SUVs have recently seen a sharp rise in popularity among enthusiasts, and it’s easy to see why.

Along with debuting a shift on the fly four-wheel drive system as a replacement for the C/Ks’ manually locking hub setup, the OBS era also ushered in an independent front suspension on for 4x4 models that significantly improved on-road drivability. Meanwhile special edition models like the Chevrolet 1500 454 SS gave the platform legitimate street cred at a point in time when performance was still slowly clawing its way out of the Malaise Era.

But perhaps most importantly for today’s hot rodders, OBS pickups now exist in a sweet spot where they’re old enough to be inexpensive, but not so precious that they command a Square Body-like premium. They’re also new enough to have relatively modern factory-equipped features and amenities, and there are still a ton of clean examples roaming the streets of America today.

“I think that for a lot of folks, it is sort of the truck version of a Fox-body Mustang,” says Bryan Grigsby, the Director of Holley Performance’s Modern Truck and Off-Road divisions. “It’s one of those situations where maybe you really wanted one back in high school but couldn’t afford it, and now that you’re a little older and you’ve got a few bucks in your pocket, the barrier to entry is much lower than it was back in the day. You can kind of fulfill that dream. And because there’s now a plethora of aftermarket parts available for these trucks, you can really have some fun with them.”

And thanks to more than 30 years of technological development in the time since, there are many different ways you can improve upon a stock example regardless of whether your goal is to have a lean-and-mean street truck, a go-anywhere off-roader, or simply a fun cruiser. With that in mind, Grigsby says that the following upgrades should be at the top of the list for any 1988 to 1998 OBS GM pickup project.

Exhaust – “If you’re starting with a more or less stock example, I feel like upgrading the exhaust system has got to be the #1 bang-for-the-buck upgrade,” he tells us. “Flowmaster has a number of different cat-back systems that range from mild to wild in terms of tone and volume, and all of them sound great with that Chevy small-block V8. And beyond the sound benefits, all of the factory systems from that era were very restrictive, so you’re going to pick up some performance here as well.”

For those who want to take their exhaust setup a step further, Grigsby also recommends ditching the factory manifolds for a set of Flowtech’s shorty headers. These headers are 50-state legal and are designed as direct-fit replacements for factory exhaust manifolds. Much like the cat-back system, they’ll also enhance the engine’s soundtrack while further improving flow and performance.

Fuel Pump – “The factory fuel pumps from this era are notoriously failure-prone,” Grigsby notes. “Anyone who has spent time around this generation of GM trucks them can recognize the sound of one of those pumps from a mile away, so that’s something I’d want to address right off the bat.”

He points to Holley’s direct fit drop-in fuel pump module as a great option to both improve the truck’s reliability and support the fuel demands that will likely increase as the build matures over time.

“Part of it is really about peace of mind – it’s a known problem. It’s also going to be quieter than the factory fuel pump, and that upgraded pump will support up to 700 horsepower. In the meantime you can just regulate it down to whatever the truck’s current fueling demands are – that way you don’t end up having to do the upgrade twice.”

Suspension – “To me, this is where you start establishing the path for the build,” says Grigsby. “Are you building a street truck, or do you want this thing to be more capable off-road? The answer to that question is going to determine how you should approach your suspension upgrades.”

For those in the street truck camp, he points to some initial upgrades that will give the truck a more aggressive look without breaking the bank.

“A nice lowering shackle kit for the rear will bring the rear end down and level out the truck’s stance. It’s a very easy and inexpensive way to give the truck a meaner look, and you’ll still have a considerable amount of clearance for larger wheels. Beyond that, you can bring the rear end down further by pairing the shackles with a replacement leaf spring kit. That will net you a drop of about four inches in total, which is about as far as you can go without having to do things like putting a C-notch on the frame in order to maintain the same amount of wheel travel.”

At that point you’ll likely want to also address the height of the front suspension to bring the front end down to the same level as the rear. Grigsby cites two options that will do the job: lowering springs or drop spindles.

“I tend to prefer drop spindles in this situation because it still allows for the full articulation of the factory suspension and it will retain that factory ride quality. With this setup you’re just moving the spindle mount upward, which in turn lowers the ride height of the front of the vehicle without changing how the suspension functions.”

He also points to the Baer Brakes Bump Steer kit (pictured above) as a way to address some of the shortcomings of the factory suspension geometry while reducing the bump steer characteristics that often become more prevalent when these front suspension systems are modified. The kit changes the geometry of the front outer tie rod and replaces the factory ball joint with a spherical Heim joint in a billet aluminum adjusting sleeve.

For those who’re looking to build a more capable off-roading or overlanding machine, Grigsby say that while the platform’s design inherently limits what can be done with a factory-style setup, builders do have options.

“The approach that’s popular these days is a long-travel suspension system with replacement upper and lower arms, which will both correct the geometry and give you some additional track width, while a lot of the folks who’re doing more trail wheeling will just swap over to a straight axle setup up front.”

But if you’re not ready to bust out the Sawzall just yet, there are some other upgrades that will tangibly improve performance beyond stock and provide additional clearance for a larger wheel and tire setup.

“The easiest and most impactful upgrade you could make to the factory suspension would be to replace the factory shocks with a nice set of direct fit gas-charged monotube shocks, along with adding a front torsion bar key. The key allows you to bring the front end up so it’s level with the rear’s factory ride height. It will give you another couple of inches of suspension travel, too, and allow for the fitment of the larger rolling stock.”

Brakes – “Regardless of whether you’re building a street truck or something that’s geared more toward off-roading, brake upgrades should be on your radar,” Grigsby says. “We’re installing a larger wheel and tire either way, which means more rotating mass, and we’ve given the truck more horsepower, so we need to improve the stopping power with some upgrades from Baer as well.”

While Baer has comprehensive big brake kits for these trucks that will deliver road course-ready performance, the company also offers more affordable direct fit options that will tangibly improve braking capability above and beyond the factory setup.

“Stepping up to a Claw performance rotor and brake pad will give you more initial bite and manage heat more efficiently than the factory stuff,” he says. “And because we’re managing the heat more effectively, you’re also going to get more consistent brake performance and better pedal feel during spirited driving.”

Maintenance and Restoration – Although these trucks feel significantly more modern than their predecessors, many of them are more than three decades old, and that means some basic TLC can go a long way toward improving curb appeal and restoring performance that’s been lost to time.

“Something as simple as the Accel tune up kit can really make a difference,” Grigsby says. “This kit focuses on ignition system components like the spark plugs, wires, and distributor cap, and if those haven’t been changed since the truck was new, you’re likely going to notice a smoother idle, better throttle response, and a bit more power, too. But more than anything, it’s about ensuring that you’re starting with a solid foundation even if you don’t know the full history of the vehicle.”

Meanwhile the folks at Brothers Trucks offer a wide range of interior and exterior components that will spruce up the overall aesthetic. “Even with a really clean example, you’re likely going to find some things in the truck that have simply worn out over time, and replacing things as simple as the sun visors or a faded and cracked dash can make a substantial difference in the truck’s overall appearance.”

Grigsby adds that it’s important to keep the end goal in mind when embarking on a project like this, as it will guide the decision-making process throughout the build. “Decide what you want the finished product to look like early on in the project. That will significantly reduce the chances of having to spend money twice because you’ve discovered that an upgrade you did a while back isn’t compatible with another one that you’re about to do, and things like that. Doing the homework ahead of time will definitely pay off in the long run.”