I have a 1999 GMC C2500. Put a new engine and got the truck running again. For some reason it feels like it has no power, gas milage is about 12-13 mpg. I have change spark plugs, wires and also done injector cleaner. Check fule pressure and stay right around 50 psi. No engine lights is on but the truck still feels lazy. oh, I also installed a new K&N cold air intake.