It's an engineering flaw. The rear wheels are hopping and causing the tires to chop across the tread pattern and making tires go out of round. The rear pinion angle doesn't match the front transmission output shaft angle and the rear control arm setup is jinky.
Any further updates on root cause or causes? I went through a similar situation with Chevrolet on a sedan. Lemon Law. Settlement. Kept vehicle but then traded it back in. Considering a RAM purchase and will most certainly exercise it on the interstate on a lengthy test drive prior to buying, so thanks for all your efforts. Also...
I will say that, during the ordeal, you're so psychologically in-tune with vibration detection that you develop super-human abilities without even knowing it. On almost every similar vehicle I test drove (test drove 8 similar vehicles), I could 'detect' the issue...but I had to train others recognize it in the more minor instances. My point is that because you're getting screwed out of so much time & money, you obsess over it and subconsciously amplify perceived issues. If you were in a different state of mind a week or so later, calm and happy with a full refund and a day full of good news, I'd bet the issues wouldn't be as bad. Not saying it's not real, just saying the stress and anger DOES take it's toll. It certainly did for me.
My lessons learned are to go legal ASAP, as dealers and manufacturers are incentivized to minimize your concerns as much as possible, and many dealer/manufacturer relationships don't allow for much, if any, profit or $ incentive for dealers to help you 'hunt.' It makes more sense for them to make you another dealer's problem, since they view themselves as victims of your lemon too and would rather someone else deal with it.
If you want to stick with RAM and it's worth it to you , I would go test drive at least 5 or so new RAM vehicles and apply your acquired perceptions to each. If you detect issues with say 3 or more of the 5, then either your newly-trained threshold of perception is too keen to ever be happy with one of those trucks..or...they literally do all have significant issues (less likely but still possible).
I hope your legal case goes well and gives you some much-needed justice. I slept like a baby the night I got my settlement check. Didn't so much care about the money anymore...it was the JUSTICE.
Cheers,
Devin