I did read that you cleaned the vent, so the may be something that you have already done. I had to remove the back cover, go in and remove the rubber extension between the washer/dryer and the outside vent to find that lint had built up enough that the 4inch hole was no longer open enough to stick my finger in. Once I cleaned that, the dryer worked great.
The only time that I watched anyone back up with the toad hooked up, he left the steering locked (by leaving the key in the off position)and it worked quite well. Once he got to where he needed to be, he unlocked the steering and away he went.