03 F150 4x4 4.6 Automatic

Feel a vibration at 60 mph, seems to be getting worse (used to only feel at 65), and now feels like driveline knock (single) after coasting, like downhill. Feels like front or below middle, but not entirely sure.

Alignment and tire balance done, front/rear u-joints checked. 4x4 vacuum shifter still appears to switch fine.

Not sure if front differential, transfer case, or transmission?

 

Almost sounds like a spline issue off the transmission going to the driveshaft.

 

Original guy that checked front u-joints probably did not! Reached under while changing transfer case fluid and found serious slop on driveshaft. Replaced both and now no more slack or vibration.

 

Well, now you know who not to go to for mechanic help!