Do you know anyone with a set of tires on their car/truck that would fit yours? Try mounting their tires on your truck to see if the vibration goes away. This would/should eliminate your tires as the cause of the vibration. Have you put your truck on a hoist and run it up to vibration speed? If it vibrates you have eliminated the front end components because there is no movement in the steering and the front wheels. The only components moving are the drive shaft and the rear wheels. If it doesn't vibrate, you have eliminated your drive shaft and rear tires. While it is up in the air and running and it is vibrating, you should be able to see something that is not right. My $.02.