06 F250 4x4 with new Hankook LT275/70r18 all around. Rear bounces like tires out of balance at 48-52mph. Had tires replaced on rear & it still does it. Front tires do good. Should I rotate tires or is something else wrong? Had rear tires balanced again from a different vendor & he said they were out only a bit. I'm starting to think something else is going on.
Thanks

 

Best way to find out would be to bring it to a shop so they can tell you for sure