Steve, thanks for chiming in. My manifolds where sent out (by me) to be milled and where perfect prior to the new (and improved) gasket installs. I am inclined to agree with you on the mechanic re-using some old parts i.e.:bolts etc. I felt like the "Cummins mechanic" was trying to get as much out of me(or the P.O. ) as possible but that's another story. As stated a lot of my cruising is done at 800-1000 rpm's and I was under the impression to not "push" them as to not blow the gaskets but now I'm not sure what rpm is better for the motors? I will agree that in 2 seasons of approximately 300 hours they have run flawless. The maint after 1000 hours is minimal, I swapped out the air cleaners for tony's and 1 set of impellers. Annual oil samples come back excellent and both motors are like twin brothers. I wouldn't go abusing them however so I will remain in my cruise parameter and hope I'm doing the right thing.