vibration/shudder

[twoiron]

I have 99 Ranger,2.5L.4spd.auto.My problem is a vibration starting at about 35mph on up. I have put it in neutral while driving and the vibration is still there, also sometimes I get a shudder when it shifts into 4th. under heavy acceleration (passing,entering freeway,atc.). I've checked the u-joints which are tight and can see no obvious damage to the drive shaft. The only thing I did notice was free play in the driveshaft at the differential yoke. How much freeplay should there be? Anybody got any ideas?

 

[93_RangerSC]

Well this might sound kinda dumb but check for mud caked around and inside your rim. might not sound like much but i thought the same thing about free play in the driveshaft but then i saw a bunch of mud caked around my passenger side rim washed all the rims and it drive fine