My driveline makes a loud clunk when shifting from rev to park etc. It has never done this befor so I climb under there to check the U joints (Thats the classic sound it makes) but there find but there is a lot of movement in the drive shaft TWISTING action. I can't tell were the sound is comeing from. I know my tranny is on it's last leg could that cause exsesive slack in the drive line and make a clunk noise? I jacked up the back end to check the axle and when I move one tire there is about 2.5in of slop befor it moves the other tire and the drive shaft. Does that seem alot to you? I did take it to a shop and they had no idea even though they heared the noise also. They seem to think I needed to add a gear additive for the locker. I told them it doesent call for it so they looked it up and I was right but they said add it any way. 03 4x4 suburban.
HELP

 

It looks like it's the gears. Would the G80 locker have anything to do with the slop?

 

that's what its supposed to do, maybe not quite to that extent, but it waits till the other wheel slips, then locks in. If I were you, and had to replace the gears anyway, i would put in an eaton or auburn or some other good quality limited slip.