I replaced my injectors with rebuilt bosch OEM injectors at 148,000 because the RPM's would lag and stick when reeved up. immediately after getting it back the milage start to fall. It went from 18 to 13. I took it back to the shop and they said its just a problem with cummins. I installed a edge milage max tuner and saw no change in milage. I very very rarely get the engine above 2K RPM's even when accelerating. if I do step on the fuel pedal it blows black smoke. Any Idea's I now have 190,000 on the engine.