Wow.. I was honestly expecting a "Hey, my truck vibrates when i hit 92MPH... Why??" (you'd be surprised what some people ask... haha)
Anyways, I would check the wheel balance, and brakes. Could also be a drive-line balance issue, but I have my doubts on that.
First question: When you press on the brakes does the pedal pulsate?
Second: what shop did you have the tires put on at?