It could be one or more tires being worn badly or even defective, or a damaged rim.
If there wasn't much to correct in the alignment, then it might not be uneven wear, but if if it did need a lot of correction, the tires would have to be replaced in order to finish solving the issue.
A tire rotation might help minimize the issue or at least narrow it down to one defective tire if that's the case.
Then again, it could be the highways. I don't know about elsewhere, but Colorado DOT seems to be slacking on some highway resurfacing, resulting in some that have absurd ruts. One of the highways I travel on a daily basis has gotten so bad that I was certain my front tire on my motorcycle was punctured and losing air, but when I pulled over, it was just fine. It's just that a stretch of road a few miles long has such serious ruts that it messes with the handling, and even the T4R pulls around a bit too...just not as noticeably. But since I noticed it on the motorcycle, I'm a bit more aware of it in the truck too.
