I have had to replace my old 6.5 Diesel (with numerous slapping fan belts which added to to the noise generated by this motor), due to Antifreeze getting into my oil. Instead of ripping this apart in the cramped space of my M998 engine bay, I chose to pull and replace with a newer upgraded A2 NA, serpentine belt 6.5 motor, basically a slightly used motor from Uncle Sam. This did not come without its problems....the injection pump was shot on this "new" motor but unfortunately, I did not know this until the A2 motor was installed...off with the intake manifold....with that fix made, I cranked her up...ran like a brick in my wife's dryer.......after replacing the injectors ( THAT DIDN'T FIX THE PROBLEM) the only thing left to check was underneath the valve covers....passenger side was the first (easiest side to check) no issue...the drivers side.....the plastic bushing was broken which held the rocker in place...the rocker worked off the valve and the pushrod was stuck in the block ..... ran stainless steel bolts wih nylon lock nuts through all the pushpins and put it all back together...has run like a bear for the last 2000 miles so far...10 times quieter along with the 4L80 I added and it drives like a dream...new motor with an A2 wiring harness, an upgraded 200 amp alternator (with 12 volt spliter), The 4L80 was the biggest and best upgrade I made.....less noise, lower RPM, I can actually have a conversation now while driving down the road at a comfortable 55 MPH...Drives down the beach in Hatteras NC like a Ferrari on the interstate.