got a 99 2500 with a cummins(manual). losing power after 3rd gear at about 2100-2600 rpm. had it looked at and they told me the injector pump is going out, $1200 part!! anyone have this problem and if so where did you get your part and how much. also been told it could just be the relay pump that goes up to the fuel filter and that it could also be that the turbo is going bad. 124,000 miles on the engine, thanks!!