2000 GMC Jimmy 4 x4 ride has gotten very bouncy and loose around corners. I had 2 heavy duty shocks added last year, but still really bounces on bumps?

The 'clunking' sound seems to suggest a broken spring instead of a broken shock absorber. It may be easier to test the shock absorber while it is still on the vehicle.
First have a close look at the shock absorber. Faulty ones usually leak and look oily and dirty.
Safely jack up the vehicle, place it on axle stands and remove the wheel. Check the spring and all the rubber bushes on all the suspension links. Any worn, perished or damaged bushes can cause 'clunking' noises. Repeat this for all four wheels.
To test the shock absorber try using the 'bounce' test. With the vehicle on the ground and the park brake on. Go to each corner in sequence. As a truck is larger than a car you may need a helper. Using your body weight, get the suspension moving up and down. It should be difficult to do and when you stop the suspension will settle quickly. (Up, Down, Settle). Try this on each corner. Soft or bouncy corners will suggest a worn shock absorber.

To test if your shocks are worn, go to each corner of your vehicle, put two hands on the car, and now pump the corner down hard a few times rapidly, trying to get it to bounce, than quickly let go!, If the car only bounces one or two or three times and stops, they are fine, If any one corner bounces more than two or three times and keeps on bouncing like 5 or 6 times, it's a worn shock. Worn shocks can make it feel like your driving a big ol' loose boat across the road, even in a small vehicle with movement both side to side and up and down, so can worn or loose body bushings, worn suspension parts, under-inflated or broken in or worn out and softened tires. If your ride height seems low it could be worn springs, Shocks are cheap and easy to change, especially the rears. Springs aren't cheap and can be a pain to change on some front ends. Good luck!

Are you sure you had the correct shocks installed?

replace the shocks with better ones not very good center of gravity in the rover

It sounds like a ball joint is worn, possibly the rack end ball joint or tie rod end.
With the bumpy ride it could also be that the front shock absorber has failed.
Jack the front wheel up on each side in turn, grab the wheel at each side and shake it back and forth as hard as you can. If you hear or feel looseness, the problem is in the steering, as above.
Then shake the wheel while holding it at top and bottom. If you feel looseness then, the problem is in the front suspension wishbones.
Repeat this on the other front wheel. Let it down on the ground, then bounce each front corner up and down as hard as you can (you might have to have a second person with you doing this). If you hear a clunk or feel excessive bounciness, it is the shock absorber. When bouncing like this, the car should resist, and not keep bouncing when you let go.

The best shocks are the ones that will handle the loads you want to give the truck. Normal driving and occasional loads can be handled quite well with a regular heavy duty shock. Most people with trucks can get by with this kind of a set up.If the ride is a little stiff when empty throw a bit of weight in the back. No name or generic heavy duty shocks will not last as long as name brands so let your budget be your guide. Cheaper shocks need replacing more often.
If you have an assortment of jobs to do with your truck, ranging from daily driver to 2 or 3 weeks of hauling a trailer to bringing home a load of top soil then you may want to look at an adjustable shocks or coil overs. These can give you the security of being able to handle the heavy loads when you need to but will compromise ride quality when empty although the adjustables wouldn't be as bad for ride. Hope this helps.

well, how did you check struts. removed them and did a compression stroke test? Front or rear? both? suspension controls ride stability, shocks,struts,springs, bushings,wheel balance. even if parts look good doesnt mean they are. bounce trk from the outside. does it keep bouncing for a few or does it bounce 3 times or less depending on how hard you jumped on the bumper. Im sure you need new struts or shocks if it is bouncy.

monroe shock and strut recommends 50k miles for shocks, 80k miles for struts. but they sell struts. if they are visibly leaking, with an oily film building around top of strut, replace them. if the tires are cupping in the center of the tread, replace them. if the car seems to have a bouncy ride and take a while to settle out after a large bump, or if you push down on each corner of the car above the wheel and it bounces easily, they probably need replacing

no, your shocks are not air. they are worn out. when you are by the car make it bounce by pushing on the bumper several times fast. If it continues to bounce 2 or more times then its time for new shocks. My avalanche is doing the bouncing thing now. Just dont have the money to replace the shocks yet.

The grinding from the brakes is probably the feeler on the pads letting you know they are about to be worn out. The feeler scratches the rotor to make the noise. When the noise stops then the feeler has broken off and you are about to be brakeless.

It's time to replace the rear shocks. There expensive like $250.00 and up each and if your not going to be towing, most people replace them with a good set of shocks and not the factor OEM air shock which you have for the auto ride height system. If your going to just buy and good set of normal gas shocks. Pull the fuse to     the auto ride system so the light on the dash is off.
Good luck and hope this helps. The auto ride system was there for towing heavy trailers to keep the ride hight. The rear suspension is actually soft so you have a soft ride and the shock keeps it from bouncing. If your not towing heavy or carring heavy loads, you should be fine with a conventional gas shocks and you may find it better. I found the Monroe Reflex shocks to be more stable then the OEM around corners and highway driving.