on any of these trucks you can jack up the rear end and there will be (or normally will be) some slight push/pull play on the rear wheels, not sure how much is normal is in "how many mm", it's also why if you go to pull the axle you may have to push the axle in to get the clips off. they are not bolted in like a front hub.
@swathdiver is usually good at providing the little details of how much play is normal. The general rule of thumb though is if it is not making noise and not leaking you are good to go.
If you are turning corners and can hear a distinct "clank" noise from the rear end and if the play seems excessive then you might want to have it checked usually though you will see a associated grease leak around the parking brake, or coming out around the axle, usually gets on the rim and leaves a black trail or you may see it splattered around the splash guard in a circle even with the backside of the wheel. or if you are driving along a wall or barrier and can hear a grinding or moaning type noise from the back that's the bearings going out
and if you hear a snapping type noise when turning that can be the rear panhard bar worn out or not torqued tight enough, in my opinon the panhard bar should be tightened up as tight as you can get it otherwise they can make noise. other noises can be rear sway bar bushing or end links, pinion bearing, driveshaft, u joints, no gear oil in the rear diff because it all leaked out, broken rear diff but when they break that usually puts you on the side of the road waiting for a tow.
I had a gammut of rear axle issue's before...
