I just talked with a guy here in our RV Park that tows a 40' 5th wheel with a boat behind that with a 2011 F350 SRW 4x4 with a 6.2L gas. He gets about 6 mpg towing about 16 empty. He has 28,000 miles on it. He says it has the power a bit off compared to a diesel in the hills. He pulls from Utah to Arizona.
He likes it & after several 7.3 diesels he feels as you do, way too expensive, extra $5000-$6000 option, diesel is $.50/gal higher than gas. then add the additive @$14/qt, The new diesels are not getting enough added mileage to offset the costs. These are his words not mine. He daughter works for Ford so he got special pricing.
Hope this helps.
Craig