I just got done pulling a trailer from Kansas City to Orange County, CA with little problem. 5 x 8 enclosed cargo trailer with a 3,000 lb. GVWR. Had it about half full but it was some heavy stuff like an old welder, steel framed mini-bike, and some antique furniture.
Well, there was one problem... Cross-winds caused a lot of trouble with near overheating and terrible fuel consumption while going across I-70 in Kansas.

On most fuel stops I was getting between 19 and 20 mpg (compared to my usual 25).