I used to work for a shop that used them for injection pump/injector rebuilds and had pretty good luck, it was all stock stuff. This was back in the mid to late 90's.
My dad was looking for better fuel economy for his 7. 3 back in '01. They had a 'chip' that was going to help with fuel economy. Dad had them put it in, and then it made the transmission shift very hard, made it hard to start, check engine light was on all the time, and it sounded like the timing was too high. Didn't gain much if any fuel economy. Dad went back to them and they really did not want to stand behind it. They finally took it out and refunded him some of the money. He was supposed to live with the check engine light on, and the rest.
Now, since then we have purchased a rebuilt turbo from them for a 5. 9 cummins last summer and that was fine. They were the only place we could get one quick.
For a local shop I prefer going to George's Diesel in Des Moines. He has done alot of pump work for us in the past. Cool old guy too.
The experiance with the "chip" put a bad taste in my mouth. Later on that year George said he could make the fuel econmy better. Sold dad a "super chips" programmer and set it up for economy. The truck gained 5 mpg across the board. Its also no slouch performance wise too.
That is my limited experiance. Maybe they've changed salesman?
Michael