you have to take the good with the bad
if you use your 2500 for pulling a trailer, then you have the best rear end ratio
if you didn't pull the trailer, different rear end ratio would give you better mileage
I have a 2009 Ram SLT fully loaded, HEMI, 3.55 ratio rear end, curb weight was 5300 pounds
i always have heavy tools & tool boxes in the bed, bringing the driving weight up to 6300 pounds
i get 17.4 MPG highway
the truck below is a diesel & he gets 24 mpg highway !!
this is his Sons truck