Having driven the F150 V8 5.0 pulling the LE 1 and now pulling the LE 2 with a F250 6.7 I can honestly say there is no comparison between the two and the overall reduction in driving stress with the diesel 6.7 has been a big win for us. Our F150 pulled the lighter LE 1 trailer fine and got between 13 and 17 mpg with varying hills and/or head winds. The best number we got was when driving the Natchez Trace Parkway (50 mph and no stop signs for hundreds of miles) during our last trip home from the Oliver factory. So far, we have put about 10K miles on the F250 pulling the LE2 trailer and have been averaging around 16-17 mpg going speed limit speeds on our trip back to Texas from Oregon and a couple of trips to Colorado. The biggest win for me along with the additional torque the diesel engine provides is the awesome range we get with the larger fuel tank and higher fuel mileage (over 600 miles). I have only had to fill up the DEF two times since purchasing the truck about 12K miles ago given that the DEF was low when purchased. We have offset some of the fuel costs via our fuel discounts we get via the OpenRoads program, Good Sams and the Bucee's 5% fuel discount for local purchases as we have 6 locations near us. Overall, I would say we use about the same as we did using our F150 to pull the LE1 as we currently do pulling the LE2 with the F250 from a cost basis. One additional lesson we learned during our trip to the Grand Canyon in the F150/LE1 was that the 5.0 engines does not like the lower octane fuels sold in AZ as their normal grade. As a result of excessive engine knocks, we had to purchase the premium or mid-grade to keep the engine knocks down to a minimum.
If I had to purchase another Truck today I would definitely go with the Diesel 6.7 as it has been flawless for us. In addition, the exhaust break on the F250 has been wonderful when going down those steep grades in the mountains as well. From all my reading tho, you need to stay on top of having the oil changes done regularly as well as the fuel filters changed about every 10-15k miles.