I pull my 7x14 brimar heavy duty dump trailer with 2' high wood sides on top of the 2' high metal sides loaded about 7' out and about 4' high with grass/leaf mixture and the scag cheetah in there with the bagger system and get 12.3 mpg and that's using my underpowered 7.3 powerstroke, with a bad injector or two. the trailer empty is 4000 lbs, the mower is easily over 1000lbs with the bagger on it, then another 2000 in grass clippings and leaves if not more.
fully lic. and ins. 10yrs exp.