Loose feeling when going over bumps

what do you think it worn with the suspension, when I go over bumps and imperfections in the road, the car rattles and feels very loose. Harsh ride. I have Bilstein shocks with thick sway bars, could this cause the issue ?

Any common problems with these cars ?
Had that same issue with my 87 GN. Fixed it with SC&C heavy duty front triangular frame brace, umi's rear upper shock mount brace, all new body bushings to include the "missing" GNX bushings, and TinMan's behind the back seat GNX brace. Made a huge difference. No more rattles and car feels tight. FWIW

you have new thick sway bars with new poly bushings I would imagine. So you are forcing the weak link (old bushings) across the entire suspension to work harder and give out.
Is this something that just started happening or has it progressed over time? How many miles in the car ? What is the rest of your suspension ? Is it stock?
There are many variables at play here , Johnnie cover most of them. I would check over all the body mounts and replace them if they are old and or missing. Make sure to do the Gnx bushings also.
Check all the control arm bushings. Then I would definitely start adding some bracing as already mentioned above.

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The car has always been like this since I've had it, it also has ATR springs with the rear air bags. the car has 176,000 miles !

I already have all the Kirbans front and rear bracing