Sgt. Peper

I got 10 MPG on slightly flat ground pulling my 26Ft toy hauler from Phoenix to Rocky Point Mexico. 150 gal of water and no ATV's. I got 10.6 coming home without the water. Not much head wind. Got 7 MPG with 30 mpg head wind heading west towards Tucson from New Mexico with the same trailer and no water or ATV's. I pull with water and two quads up from 4000 FT. to 8000 Ft and get 6 to 7 mpg. I pull home with same load and get 14 mpg. I run stock tries, 373 gears, pull at 65 mph when I can with automatic and less than 10,000 miles on my truck. I pulled at flat bed car huler from Phoenix to Kansas City empty and got 14 MPH at 70 to 75 mpg. I came home with a 34 ford street rod at 65 mpg and got 14 mpg. Not much wind drag and not much weight. I will pull this same trailer to New York and back with very little water and gas in gas takns next June (over 5000 miles). I will do a complete mileage caulation for that trip and post it when I get back. And I don.t lie on mileage. The best I have gotten so far id 20.6 and that was from 8000 ft. to 4000 ft. not pulling a thing. 2WD and six speeds will do better as will a truck with over 30,000 miles.

Pop-Pop

I just returned from a 10,000+ mile round trip from VA to AK via the Rockies (including the Canadian Rockies). Lots of really steep grades & lots of poor roads where I had to drive 30-35 MPH. Pulled a 25' TT and had lots of weight in the truck. Max driving speed was 65 MPH. Never a problem getting up the steepest grades. I averaged 11 MPG (hand calculated). Interestingly, the overhead showed exactly the same average MPG as the hand-calculated number.

supr

Given all tires are aired up to max, 50-55 is an optimal speed for mileage. At 55, I can achieve over 13 mpg, flat land, not much wind, with a 36' long, 12', 14k fiver. If you can live with slower speeds, better mieage will result. 65 will suck 20-30% more fuel than 55. Carry only 1/3 tank of water, fill up when you get close to where you are going or just hhok up at the camp ground.
Wind resistance is the biggest issue to decent mieage.

rich

in the 03 towing the trailer it weighs 8k i get 11 to 12 running 70 to 75, with a load depending on the height of the load not so much as the weight i get anywhere from 6 to 10. with the wifes truck i went to iowa with the same trailer and empty i got about 13 @ 70 and loaded with about 3 ft tall load weighing about 18k i got right around 9.75 to 9 so gross weight was about 33k 03 has 3:73 rears and is 4x4 5spd while 98 is 3:55 auto 2x4

SupaDupa

We've got the same trailer and I get about the same mileage you do!!! I'll get 15-16mpg at 65mph if I'm not bucking the wind or doing a lot of hill climbing. I've got an 04.5 also!!! My trailer loaded runs about 5k.