Swaying from the rear.

SOURCE: seems to wander at highway speed almost like the

try to change the bearings

SOURCE: Install rear sway bar

a sway bar is usually u shaped and hooks to the body and the tops of the u hook to the axle with links that have bushings. most jeeps dont have a rear sway bar.the panhard bar is the rod that goes from one side of the axle to the body on the opposite side. its sometimes mistakenly called sway bar. it keeps the body from moving side to side around corners. then there are the torque bars they keep the axle from trying to rotate when accelerating.
none of this would be real expensive but if its been lifted a bunch then you may have problems

SOURCE: There is a swaying in thr rear end of my 99 jeep

Unlike other Cherokees, you have coil springs in the rear, not flat springs.
Coils tend to react more to side loads and will therefore sway on turns more than a flat spring will. You need to look at the attachment arm bushings and mounts to make sure nothing is worn or loose.
Its very likely that the only thing wrong is that your shock absorbers are worn out. From the outside even ones that have failed don't look bad as the failure is internal.
When buying shocks, get the best ones you can afford. they last longer and control movement better. The more expensive ones tend to have larger pistons and better internal valving that translates into better control and longer life. If you carry heavy loads, I'd consider getting "coil over" shocks that also offer a bit more load carrying capacity.

SOURCE: When I drive down the road my 97 Grand Cherokee feels like the back end is swaying from side to side

I would take it into an alignment shop