Common issue with auto trucks. you need to do a couple of things to make it less clunky.
1. adjust your rear brake shoes, if your brake bellcrank (parking brake cable arm) on the backing plate moves over 1/8" adjust your brakes till it only moves 1/8" when the parking brake is applied.
2. remove your driveshaft, mark your "phase" of the slipyolk, seperate the slipyolk, clean all the old grease out and inspect the splines, if there is a sharp edge on the tip of the splines file them down smooth and rounded, find the best molybased grease and lube the shaft, line up all your marks and reassemble, grease all your u-joints, grease the slipyolk through the zerk being carefull no to add too much and put the splines in hydrolock, drive and see how it feels.
If that doesn't work you might need a rebuild for spline wear.