First off let me say this is my first post, and Thank You in advance to anyone who might have any input on this what so ever.

Well I have a 2004, f250 crew cab lariat. Straight axle with 7 inches of lift on it. It has a 5.4 motor and an auto transmission 3.73 (never re-geared), and comes equipped with the 2 piece drive shaft which was shimmed with the carrier bearing (but has never been right, always had the shimmy from the git go).

She had 37" toyo muds on her on for the last year but just replaced them with 35" at's which are way lighter.

Now for the problem.. While I had the 37's on they were heavy and the truck shifted ALOT, back & forth all the time. Now when it shifts there is a grind / vibration under your rear almost makes you think the truck is gonna explode.. especially when the boat is hooked up, or goin up a hill. now since I took the 37's off it has gotten better, but it still does it. sometimes quite bad, and through out the entire length of the shift..

I have had the transfer case looked at, and the rear diff looked at and the synthetic looked new still. I have no flashing lights on my gear shifter which (please tell me if im wrong) should indicate transmission problems. so would this maybe be drive shaft, u-joint, carrier bearing problems?

Please if anyone has any thought, let me know.

Thank you in advance,

Jake



there are 170,000 miles on it right now, not sure if that helps.