Stumbles on accel until 2500RPM, gray smoke, electonic pressure control reads 0
1997 F250, 280K miles, manual trans. Truck idles a little rough, and stumbles until 2500 RPM, belching gray smoke until 2500RPM. Under load in 5th gear, truck will run perfectly above 2500 RPM. No codes, put scanner on the truck while running and the only thing I can see that doesn't seem to be right is the electronic pressure control value never leaves 0. The way it runs under heavy load at higher RPM makes me think there is nothing wrong with the engine, turbo, or injectors. Any suggestions??