Vibration in drive line when decelerating at speeds of 35 mph or more. I can feel it in my manual 4 wheel drive shifter. Rear end (8.8) just rebuilt. This F150 has been doing the job of an F250 for some time.

Does anyone have a thought?

 

You probably ruined it then. Thanks for admitting that.

 

Your description sounds like a bad outer pinion bearing/flange etc. It could be a u-joint, but that should be evident in power as well as decel. I'd drop the 4 bolts that hold the driveline, and check the rear end (wheels off the ground of course. I'm too big to fit under, otherwise, lol) flange, to make sure it is not loose. That would be my very the first thing to check.