my 2012 2 wheel drive suburban bumps hard while stopping sometime

There's a few things that can cause this issue. However; I have a friend with the exact same vehicle only a year older. His was making similar sounds also while driving back roads (bumpy). Turned out the front shock had a broken mount assembly and was basically clicking against the mount on the body. Check that to see if there's any issues with the shocks, then the control arms as well. May be a busted bushing in there somewhere. Something bumping and you can feel it? Then something is moving that isn't supposed to be.

Not like any part of the suspension but rather a hard bump just as the car is stopping, even a smooth stop on a smooth road and feels more like something underneath is pushing the vehicle as it is stopping! Almost as though I have been hit by a vehicle behind me shoving the vehicle! The first time it happened, it was quite a surprise..

Sounds like it's possibly a brake locking up in the rear? But more like something in the suspension moving and thudding. Check the springs, struts, and believe it or not it could be lose mounting bolts to the rear springs. Check them all; give them a good look over. Look for really shiny metal. If you see really shiny, it means wear, which means not good in anything.