The truck... as in my signature. I've towed a 16' single axle "landscaper's" trailer and 28' gooseneck horse trailer (heavily loaded with camping gear). The mileage goes down noticeably towing the landscaper's trailer & more with the horse trailer... but nothing like with the new-to-us toy hauler. With the TH, straight highway running, I was down in the 9-10 range. The rig seemed to have a lot of drag. Even down hill, it would not "coast". If I lifted my foot, the speed started dropping at once.Late last year we bought the ToyHauler... "28" foot (only includes the box, +3 with the A frame). It is well used & has a Salvage title. Definately not a virgin, there are signs of body damage on the front wall. The rear beds are gone & we only have my electric mobility scooter in the back... it is seriously nose heavy. It is a tag-a-long with a much needed load leveling hitch... I've gotten that part figured out. The trailer is high & has a FLAT FRONT, with just a small radius at the top. It has the aerodynamics of a brick.I was thinking that it was just the aerodynamics... but I'm wondering if there's something else. I think I need to check out the wheels before it goes over the road again. Electric Brakes Wheel Bearings Something could be dragging.