my 2002 2500hd diesel won't go over 1500 rpm. what could be my problem

does this include in gear? many newer vehicles are including a band limiter for when it is not in gear, to help protect the engine

only under load. in neutral rpm's are fine

just shooting in the dark here, but are there any codes to point in the right direction? sounds to me like a variable-timing issue. does the problem occur during a brake-stand? another thought, is it shifting correctly (automatic) the engine's computer may be trying to protect itself.

no service lights. did not think diesels had variable timing. did not try brake stand. hard to tell if shifting because of rpm issue. however when shifting manually same problem. 1st gear will hold to 2000rpm after that all other gears 1500 max and not over 25mph

Your fuel filter may be clogged, I've heard that if you use lower quality fuels, your fuel filter will clog and your truck will go into 2000rpm lockdown and won't shift.

I have the same problem and the filter is clear clean and new too. Someone told me your transmission Solenoid might have gone out.