2010 challenger
 

Hi everyone, I'm new to any kind of forum but I'm hoping to get some help. We've got a 2010 challenger in impeccable condition however when we tow, the temp gauge goes up. It's nothing to do with brakes on the van or exceeding tow limits. We've had 3 different mechanics look at her and none of them can find a single fault. The only feedback we've given is to tow in 4th gear. So now the engine revs at 2500 and we burn fuel! We love the car and don't want to get rid of her so please does anyone have any suggestions or has anyone else experienced this before?