Hum... Maybe you have a bent rim? What kind of tires did you buy? Like brand name? Where did you buy them?
Check your wheel bearings too.
To be honest with you my old 96 1500 had a mysterious shake at high way speeds and I could NEVER find the problem. That truck had a whole new front end after I was done and it still have a shake.
I hope you find it buddy. I know how annoying it can get!
I suppose anything is possible. I only got two new tires, and they are on the front. The vibration feels like its coming from the rear, but the steering wheel shakes too. I have looked the front end up and down before and everything is fine. The back tires aren't dipped out, but the centers have zero tread left just about. I wish I still had access to a tire machine, I could just check them myself. I guess I'll just have to get two more tires and see what happens. The ones I got are Federal SS595's and are the ONLY tires I could find for under $100 ea. I would much rather have BFG, but they are like $180 ea.
Where ever you bought the tires, ask them to re-spin them, but ask if you can watch the tire spin. Tell them your looking for a bad tire or a Bent rim. Most shops will at least let you watch.
Also, don't just look for any flat spots, but look for bubbles or spots on the side-wall and on the inside side wall.
Remember check your wheel bearings too. They can definitely cause a shake.
