Ford Explorers have just about the crappiest automatic transmission ever. I'm sure U-Haul is just sick of paying for new trannys when dopey customers don't read the towing instructions in the owner's manual, then proceed to burn up their tranny because they overheated it. People who tow need to get a transmission oil cooler to help with the excess heat (this is recommended by every manufacturer and many offer it as an option). If they don't get the cooler they are supposed to follow strict weight and speed recommendations in order not to damage the vehicle. Knowing how much people "read" instructions, I'm not surprized U-Haul is playing CYA on a vehicle that is known as a shotty product.