7200 lb trailer, throws you about half what my 5er weights. I had to go with 4.10 gears and DRW for my situation. With my 6 speed auto I get 8 towing and 13.5 empty. I know others with 3.73 gears do better. I'm not sure what other gears are available, but the 6 speed could give the option of using 4th gear with a 3.42 for towing if need be. I have family with 5.3 getting over 20 mpg empty but they don't tow. The 6.0 and the 6 speed are great and I'm an old big block fan.
I think a gasser will cost less for maint. I've put over 200,000 on several with no major and very few minor repairs. You won't have the capacities of the diesel but there are a lot choices under 13,000 lbs for us gassers.