I have the same exact power train and I run similar RPM!s at 65 MPH.Don!t know if this is normal or not but I think it is.My 8.3 has 657,000 on it and still seems ok.I change oil every 9-10,000 miles,don!t beat it but don!t baby it either,keep the idling to a minimum and so on. I have met 2...