What were you seeing for mpg's?
I have made this 400-500 mile run several times now with this truck and this run was consistent with the others on fuel economy, 9.5-10.8 is what I had. Depending on the return trip.....we had a good head wind on the ride home.
WIth the 3.73s and 35" tires I am fine with that performance. This truck does well when you can keep speeds in the 63-68 mph range but due to traffic and truck traffic in the hills we found ourselves in the 55-60mph range a lot which means 3rd gear on the hills, 3rd puts you solidly in the sweet spot for this engine and it will accelerate my load easily up good grades to pass slower big rigs etc. Of course 3rd gear will drink plenty of fuel.
We towed in a caravan with a 2013 Cummins, 2009 6.4 PSD (modded) and a Silverado 1500 and the Cummins with a similar load got 12.8mpg on the same route but that also included six 10 mile trips unloaded to the hotel.
I only tracked my towing mpg, the hotel runs were normal unloaded mpg......12-15mpg in mixed highway side roads.
The 6.4L PSD had gobs of power but a more tentative driver, don't know the fuel economy but knowing the 6.4L PSD, it probably was closer to what I got in the gasser, just with assloads of torque.