I had two different first gen Cummins trucks. They are great engines. The transmissions aren't the best though, especially when you turn up the power. Many first gen trucks have been upgraded with better transmissions.
I did some mods to the '93 W250 - 16cm turbo housing, no muffler, 4" tailpipe, K&N filter and pump adjustments (more fuel). It ran strong and pulled a trailer well. The only problem I had was when towing 13K in the summer with the AC on, it would get hot in the hills. Had to back off the right pedal on the hills and watch the pyrometer and coolant temp. This truck had 3.54 gears. It dyno'd 196HP and 572TQ at the wheels with stock injectors.
The other was a '79 K30 with an early '91 Cummins conversion. This truck had 4.10 gears and pulled much stronger than the '93, with only minor pump adjustments, K&N and a straight 3" exhaust. No heat problems either. Never dyno'd it.
They are easy to turn up yourself. I learned a ton at turbodieselregister.com. Lots of knowledge and experience there. It's worth the annual fee. I've switched to a Duramax now, but still addicted to diesel. Let me know if I can answer any specific questions.
