Rear diff play

How much free play should there be in the rear diff on an 05 2dr. 4x4? I get a clunk in the rear end in stop and go traffic at slow speed braking then slow acceleration. When I move the truck back and forth there is noticable play in the drive shaft at the rear diff. There is not a lot but what is acceptable?

if you are getting a clunk when accelerating then you many need to replace the u-joints.

I just checked under the truck while I had someone push it back and forth in park, the U joints are good but the play is in the diff.