I believe that going from a 60 series tire to a 65 series tire means that the 65s are a bit taller and narrower, and therefore there should be less rubber in contact with the road and less rolling resistance, for what that's worth.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Teddy (Jack Russell terrier)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.