I have noticed that any one that offers a fuel card is usually more expensive to start with. We use gas buddy and locate a reasonable fuel station, we can find a cheaper per gallon station within a few exits and still fuel up at a quality station, I won't fill up at a non busy, back woods station, always something that will sell a lot of fuel. We keep our speed around 62-63mph also. I have tried it all, 5th gear, a little higher rpm, some say this helps, me, I keep it in 6th, usually gets into 6th just at 60ish. I set the cruise and let it eat.
2006 2500HD CCSB 2WD 2014 Crusader 285RET
Nights camped in 2013 - not enough!
Nights camped in 2014 37
Nights camped in 2015 40
Nights camped in 2016 39
nights camped in 2017 7