We have a 1994 GMC 6.5L. When we got it it wouldn't run for more than about 15 minutes before it would start bucking and spitting and finally die. After it cooled down we could drive it again for another 15 minutes. Installed new PMD and moved it to to the wheel well. Didn't fix anything. Changed the injector pump timer and that solved the problem. My husband is now traveling from Virginia to Kansas. In Tennessee started having issues so he changed the lift pump. Got diverted to Arkansas to help with the tornado and on his way from Arkansas to Kansas got stuck in Missouri where we changed the injector pump. Finally got on the road again to Kansas and couldn't get the truck over 45 mph when going up hill. Now, he was pulling a trailer loaded with about 1500 lbs. Now he's in Kansas and even without the load he still has times it runs fine, then have times he'll have his foot to the floor and only going 45 mph. He's changed the air filter. There is no smoke. He is worried he cannot trust it to make it back home to Virgiania. Any ideas on what to do next?

 

Is the LP working when the engine is running?

A non working LP is often from a bad oil pressure switch-AC Delco ONLY for replacement.
Also get the parts and install the OPS relay mod:Google it.
Or buy the kit from Kennedy Diesel and install.

A plugged vent in the filler cap or a plugged/collapsed tank sock on the sending unit also restrict fuel flow.

 

Per hubby....LP is new, only runs at 4 psi compared to injector pump that runs at over 12 psi while running. Does that sound right?

Will let him know about the OPS relay mod replacement and plugged vent plugged tank sock.

This truck was parked for almost a year before we got it and started tinkering on it. Anything that could dry rot?

 

The pressures stated are a bit confusing-the IP does not run @ 12psi-it supplies the injectors with over 2200psi of pressure,the LP supplies the IP with 5-9psi normally but that often drops under hard acceleration to near 0.

Sure fuel lines rot and allow air to get into the fuel causing driveability troubles-need to check for trouble codes,google paperclip code checking and look here for the definitions or post what codes are stored.