If you set a fence post in Jello does it make any difference if the fence post is made of pot metal or titanium? It doesn't. No matter what the fence post material they will shake like Santa's belly.
The same is true on your 5th Gens. Every 5th Gen has rear end step out and significant dynamic caster changes the moment it rolls off the assembly line.
Add bigger bars -- rear end step out becomes more pronounced.
Add stickier tires -- rear end step out becomes more pronounced.
Add more RWHP -- rear end step out becomes more pronounced.
Notice the pattern? While the IRS sub-frame bushes are far from Jello, they are deeply voided for control of Noise Vibration and Harshness (NVH). It was a benchmark for the new 5th Gen -- Library Quite. Quiet is perceived as quality. The efforts to makes the 5th Gen as quiet as the target resulted in some loss in handling qualities. No matter what you driving style, no matter what your level of modification the lowest hanging fruit on a 5th Gen is found in the sub-frame and radius bushes.
Virtually every 5th Gen suspension company makes replacement bushes, braces or bars for the IRS. Why? Because they know as we do it is the single most important upgrade you can make to a 5th Gen. If you already have sway installed, you will notice your 5th Gen drive much better with sub-frame bushes or inserts installed. Have a better than OE tire and wheel package -- you will notice your 5th Gen drive much better with sub-frame bushes or inserts installed. Increased your RWHP -- you will notice your 5th Gen drive much better with sub-frame bushes or inserts installed.
Start with the sub-frame and radius bushes. Create a robust foundation. All your additional mods will work better because you did it the right way. You started with the foundation. You can read all about it in the
Book on 5th Gen Suspension.