I have an 03 Chevy Crapalanche that I use to drag motorcycles to the track and basically nothing else. Both rear tires have slow leaks. I can't imagine I overloaded them, but it's weird the two rear ones have this and the fronts don't so that's the only thing I can think of. The most I've had in there is ~1000lbs and it supposedly can handle ~1350lbs. I do drive like a complete fucking madman if that makes a difference.