You could drive that truck from here to Florida and back in 4wd without issue except when turning sharp on pavement. So even if the lockers stuck AND you left it in 4wd it wouldn't vibrate. But you took it out of 4wd so it doesn't matter if the hubs were locked or not.
It drove smoothly at 65 so not a wheel bearing. They get worse with speed.
Really doesn't make sense. But then again neither does 4wd with a camper in the back unless 2wd is prohibitive.
Was it death wobble? Seems slow for DW, but other "issues" don't trypically fix themselves. And being a 2017, unless it has a bunch of miles, nothing should be close to wore out.
Is a bit of a mystery.