Pulling up beside a truck at a red light, many of us true gearheads can tell you what engine is in it by the way it sounds, especially if it’s a diesel. The GM engines have a distinctive sound to them. So do the Super Duties and RAMs. But if you have a GM 1999 GMC K2500 pull up beside you, your mind knows what it’s supposed to sound like. But in this case, when Jeremy Hartman from Hutchinson, Minnesota pulls up beside you, it may confuse you a little bit. You see the grille of the GMC but sounds just like a 5.9L 24-valve Cummins. Your initial reaction may be, “maybe it’s another truck behind it that I hear.” The light turns green, and the two-tone GMC pulls off but the sound is most definitely that of a Cummins. The confusion sets in, and you immediately start trying to wrap your brain around what you just heard.

For Hartman, this is a common occurrence when he drives his truck – confusion from people around you – and having a truck that doesn’t sound like it’s supposed to is par for the course for him and Diesel Conversion Specialists. Swapping a different diesel engine into a donor truck is an everyday task for him and the crew. His shop is your one-stop-shop for all your diesel conversion parts and can also provide advice when installing them to get your vehicle swapped if you are nervous about doing the wrenching yourself.

The truck you see here is Jeremy’s personal truck, as well as the shop truck. I’d say it’s a perfect example of what the shop has to offer. This truck is a 1999 GMC K2500, crew cab, short box, 4WD, ¾ ton. This truck spent most of its life in Montana cruising down back country roads. The crew cab short boxes of this era are not the easiest to find, so when one shows up that has the potential to be great – the opportunity is often too hard to resist. Hartman said, “I’m personally a product of this era of trucks. My first pickup was a ’96 K1500 extended cab I picked up while working construction – pouring concrete – just out of high school. I put that truck through the ringer, and it held up for quite a few years. Sitting in the driver’s seat of one of these GMCs is a comfort not easily duplicated. Too new to be ‘old school’ and too old to be ‘new school,’ it hit the awkward years, but these trucks are now starting to gain back their popularity.” 

For this build, Hartman decided that the 454ci gas engine had done its job, so it was time for a diesel swap. It had been said that there wasn’t enough space under the hood to accommodate for the extra length of a straight-six Cummins engine. If you did get it to fit the firewall would have to be cut open and dropped back. Or worse, the core support would have to be moved forward, and the front clip redone. He test fit the Cummins, and it was determined that the engine could fit without moving either one as long as you didn’t use a mechanical fan and went with electric. But Hartman protested, “I like the Cummins mechanical fan, it’s worked great for these diesels for years”. To get the extra room needed for a mechanical fan, a Tough Country 4-inch suspension lift was installed. The extra height with this lift allows you to not only get the engine slid back just enough for the fan, but also gives you a little more distance between the engine and the front differential.

The Dodge Cummins accessory drive has an A/C compressor that sits really low. This often interferes with the frame rail when transplanting this engine from its original frame. To get these accessories up high, Diesel Conversion Specialists makes a High Mount A/C kit. Putting this kit on the engine gives you the room needed to get it between the frame rails. The mount also allows you to keep the GM alternator. This is handy because it has an output signal that can be used to drive your tachometer. Diesel Conversion Specialists makes an A/C hose and fitting kit as well. Using this kit, you can make connections from the Dodge compressor to the GM evaporator and accumulator. Allowing you to run air conditioning. Creature comforts were limited in this era and they all must be kept. 

GM used the 4L80 automatic transmission in these ¾ ton trucks and they have proven to be a good workhorse. Diesel Conversion Specialists makes an adapter plate using an SFI 29.3 certified flex plate to bolt these stout transmissions right up to the Cummins engine. They also sell a low stall torque converter made by DPC. The transmission was moved back a few inches from the factory mount. A new front driveshaft was fabricated, and the rear driveshaft was shortened to allow everything to line up perfectly.

Delivering fuel to a VP44 fuel pump is an important job. These pumps use fuel to lubricate the internal components and when it goes dry, the pump goes bad. To supply this critical component a FASS fuel system was installed with a little bit of creative work on the 1999 GMC. To use an air-to-air charge air cooler, the core support would have to be completely redone. It was decided that the air-to-water system may work the best with the limited room. The 3-inch charge air piping leaves the turbo and routes to an intercooler under the radiator. The intercooler fits under the front skid plate. The 3-inch piping moves the cooled air to the cold side of the engine and into the factory air horn. The heat exchanger for the charged air system is placed in front of the engine radiator. This setup allows you to keep a factory GMC front-end look while being rated at 1,200hp.

The exhaust system is from Diamond Eye Exhaust. The firewall and turbo are a tight fit, so a 3-inch downpipe is used. The 4-inch exhaust lets the spent gasses flow easily out the rear of the truck. A resonator gives the exhaust a nice low rumble as it sends the expelled energy out the 5-inch chrome tailpipe.

Electrical wiring to get the Cummins to run stand alone was done through Diesel Conversion Specialists. They offer a standalone 24 valve harness for this era of engine. All engine data is fed into the factory GM cluster. Speedometer, Tachometer, Coolant Temperature, Oil Pressure, and Voltage all work the same as factory. Transmission is controlled by using a US Shift Quick4. The transmission controller comes with all new wiring for the transmission and the controller is small enough to mount right into the cab.

For the exterior, a set of weld-it-yourself Move Bumpers were added front and rear as well as a set of fender flares. The two-tone gray and white paint give this truck a classic look and really cleans up the overall appearance. 

Jeremy can be seen running around town in this one-of-a-kind shop truck and occasionally stops by a few truck shows to show off the work his shop is capable of. If you want to see more about what his shop does, check them out online on all the main social media channels or on their website.