My brother just called and said that his truck has no power at anything over 1500 rpms. It is in a 04 2500 with 88k auto showing no codes and no smoke.
On small hills it looses power and speed and just will not pull over 1600 rpms. Is it a boost or fuel problem.

 

replace fuel filter if nothing else obvious. Take to a Cummins dealer for diagnois/repairs.

 

check the boost clamps and change fuel filter then go from there

 

Check air filter also....

 

My vote is fuel filter.