Check the VIN axle ratings of the trucks that you are looking at. Any heavy duty options (snow plow, camper, heavy duty, etc.) will increase the front springs. Stiffer springs, same weight, means that the front doesn’t settle down as much. I measured close to an inch difference back in 2011 when we were shopping. I don’t believe that a 350 will improve the towing experience over a 250 for a TT only. The auxiliary springs supplied on the 350 may not even engage with a TT hooked up.