Transmission trouble?

[Plunge]

i have a 94 ranger standard with the 4.0l. when i take off in first i get a squeeky sound comming from my transmission, and at top speeds my truck seems to vibrate quite bad (side mirrors shake). Now the shake only happens when my clutch is ENGAGED.. If i disengage the clutch going down the highway i feel no more vibration. My friend thinks its the release bearing in my transmission that is shot. Can someone help me identify the problem THanks!

 

[Blacksmith1]

I would check the u joints and trans/engine mounts, just incase.

 

[Plunge]

Is there anyway to check them without taking my rig apart? can u joints make that noise?