Ram towing mileage

Got an 18 2500 Cummins on 35s, gets 14 city, 18-20 highway, depending on load 8-13 towing. She won't win any drag races or sip fuel, but towing is a dream. Really need to delete the truck. Had a 16 2500 6.4 , also on 35s, was more sporty than the Cummins but went through two brand new engines in 3 years, the dreaded 6.4 piston slap and expecting a gas engine to pull grades at 75 mph towing really didn't help