We'll be taking an 8hr trip thru the Smokey Mountains in a month which will be my truck's first real test. I expect mpgs to be even lower than normally encountered while in the mountains and to be making plenty of gas station stops. I'm just seriously expecting that this trip will make me re-evaluate my 6.4/3.73 choices. A 5th wheel was not in our original plan, but those that own a camper all know how that goes. Therefore I've been contemplating what I can feasibly do in the next year or two since longer trips are in our future.
So here's my dilema. Last year we bought a 9250 lb dry 5th wheel (so easily 10K loaded) which my truck pulls very well. When towing though the truck prefers 2nd on the hills and the mpg's can be miserable. The MDS is pretty worthless even in normal daily driving, but some with 4.10s have said that their's works better resulting in slightly better mpg's. I can live with the 12/15 unloaded around home, but my current 7 mpg towing is a tough pill when considering future long road trips. I've seen some 4.10 guys reporting 9-10 mpg towing heavy which isn't a huge improvement, but when considering either a $2500-$3000 re-gear to 4.30/4.56s or equivalent trade up to a new '17 with 4.10s (possibly a Mega cab too) I'd easliy go new.
Right now I'm just trying to get real world experience and researching my options, but if I do ever decide to trade up it'll be a Mega 3500CTD or a Mega 2500/3500 with 4.10s.