Scotty,

I have a 2019 Chevy Colorado with 20,000 miles.  This truck is driven local a few times a week and a few long distance trips (800 + miles).  I purchased the tuck new and found it to have a high speed rear-end shake.  At 80 mph the truck shakes (like [expletive deleted]).  I feel the shake in my seat and see it in the passengers seat. I have been to 2 dealer shops who talk in circles and don't seem to want to find or fix the issue but instead want to sell me tires. I have had the transmission fluid changed per the bulletin for a lesser viscosity.  Everything that has been done has not fixed the problem.  I have multiple questions, first is can you adjust the tow in/out of the back wheels of a 4x4? Second, what is the best way to test the axel angle, because I believe this to be where the nefarious vibration comes from.  Please help!!