Hi Wicky,
I am no expert but it sounds like your problem is in the Accelerator pedal position (APP) module. Our Diesels do not have a cable going to a throttle body as in gasser. Ours is a fancy potentiometer (has conditioning electronics to communicate with PCM)which talks directly to PCM. Then the PCM tells the Injection Pump what to do.
You said that it would still idle but, no acceleration. This is a good indication that it is the APP module because the PCM controls idle speed.
First thing I would do is pull the electrical connector and clean it with a good contact cleaner and check the wiring visually for any problems. If the problem still comes back. I would suspect that the APP module is going bad and needs replaced.
1997, C2500, excab, SB, 6.5TD (L56), 130,000 miles.<br />DSG Gear Set, Kennedy 3.5" Exhaust System, Killed the Cat.