My car started shaking on the passenger side when i dont have load on the motor in 5th or 4th gear at higher speeds.I looked into everything and my passenger side axle has play in it side to side and play when i twist it clockwise and counter clockwise.What could be causing all this play ? Bad diff ?

 

More than likely a bad differential bearing if its right at the trans where the axle stub goes in. Pull the axle and see if you can get the diff to move around so that you can verify that is the problem.

 

would i be able to change the diff bearing while on the car or would i need to tear the trans down

 

I wish it was easy that way but, you will need to pull the trans and open it up.