Both will squat the same as they have the identical springs in the rear. Bumpstops will kick in slightly earlier on a 37 but you shouldn't be hitting those towing unless huge dips. As mentioned, gear ratios will be noticeably better on a 35. I have a 35 truck that tows a UTV and 6,500lb camper and I recently succumbed to trying 37's and it gear hunts significantly more and the towing experience isn't near as good.