Do you still have the same "stock" rear springs? If so, with towing, the springs "settle" Kinda like a house. Spring steel has an original new hieght. but when installed and used, they settle. I would either add a leaf (but stiffer ride) or air bags would be best. best ride and could adjust to your needs while towing. I just had installed Firestone Rear leveling system with a larger pump and a 3 gal tank to opperate pnuematic tools.