Oil change and a new set of shoes. Had a set of 255/70r16 Cooper Discoverer AT3 installed today. They look awesome, and are only slightly louder than the Goodyears that were on it. Now I just have one concern. Took it about 25 miles on the expressway today and the truck feels very unstable on the new tires. Not a vibration like an unbalanced wheel, but more a general floating feeling. Its almost as if it's driving in strong gusts of wind where the truck just feels wobbly and a bit uncertain. There was a bit of a headwind on the initial trip but no gusting, and it was rough enough that I stopped once 5 miles in , when i could tell my wife was feeling carsick, to check tire pressure to be sure they weren't way off. The rear end especially feels like its moving side to side. On the way home with the wind at its back, wasn't half as bad, but still definitely there. Any ideas what could cause this?
My only thoughts were A) the trucks factory suspension at 87500 miles could be showing its age, but I still wouldn't expect such a pronounced change with the tire change, or B) perhaps one of these tires has an odd belt or something, but it seems at 75 I'd feel a fast vibration, not this random wandering of the tail end. Any advice would be appreciated.