How about some empty numbers between the two trucks? I do realize one is DEF and one isn't.
Looked back to similar driving mostly freeway the 11 would get in the 14's and the current 15 the 13's. Some tanks on both were higher but the 11 consistently a bit better. I am sure if the 15 had 3.42's it would be better than the 11 on the highway.
I never had any fuel in the oil sample of the 11.
If the 11 had the AISIN I would still own it as the trucks were basically identical.