Slack in drive shaft

[AD80]

I made a post a while back about how i get a clunk and small jerk when going from park to reverse. Doesnt do it in drive, only reverse. Doent matter if its cold or hot.  Other than that, everything is fine, it shifts smooth while driving. I just crawled under  and with the truck off and in park, i can twist the driveshaft about 1/2  or more each way.  How much slack is this thing supposed to have, is this normal?  I live 2 hrs away from my dealer and i dont want to make the long drive only to have them tell me its normal and within tolerance.  5.3  4x4 8 speed with only 700 mi.