2006 Dodge Ram 2500 shakes above 50 mph

Shakes above 50 mph.
Balanced tires and driveshaft. Checked mounts-ok.

shaking front/back/whole truck?
engine RPM related/ truck speed related?
is it worse turning left or right?
Tire balancing spin balanced/load balanced?

We need a lot more info.

Just a guess, you have a tire with tread separation that a spin balance wouldn’t detect.
Swap tires front to back and see if that makes a differnce.

I do have one tire that was new with the truck in ‘06 on the RR. The others are about 6 years old. I don’t drive it much. I don’t see how the spin balancer wouldn’t pick it up, but maybe. I could put the spare on and try it.
It’s not horrendous. Just enough to annoy you. Sometimes worse than others. Above about 50 or so.

It could be the dreaded “death wobble”.