My 2012 3500 had 3.73's & g56 6 speed manual. Lowest ifta 8.8 average of 10 & high of 10.68mpg. The g56 has a much lower OD ratio @.74 vs the auto @.63. I'd cruise around 66mph @1960ish rpm. It got the job done no problem..
Congrats on the truck.
Just fyi, spinning a few more rpm does not mean it will always get worse mpg. It all about boost psi. Get a gauge if it doesn't already have one. Lower psi generally means lower fuel consumption. Plenty of times in my ram I'd have a high sail load. Drop to 60mph for better economy, my truck was 1775rpm in 6th gear @ 60, but was too slow for the engine pulling all that wind drag at @60. Drop to 5th & now I'm spinning 2400@60. Economy would jump from about 7.5 to 9mpg even though it's spinning about 625 more rpm..
If buying another hotshot truck, that would be my truck of choice. A 4500 4.44 auto with max tow package, or 4500 4.10 with g56 standard trans..
4.44 auto should run 1950 @65 & 2100 @70. In my IMO, thats exactly where that 6.7 cummins with emissions intact likes to live on the lower less wind dragging loads..
There used to be a site, cummins spec or something like that. It said 1900-2400 was the best operating range for the 6.7l @65mph up to 50klbs gross. I believe it went like this..
1900-2050 for economy
2051-2250 for balanced economy & power
2251-2400 for power