Never used the KYB's, nor am I familiar with them, however, when I had H&R's in on my SHO, never experienced any bouncing.
I also had the stock (Non-PP) suspension in during that entire time the H&R's were installed, no issues.
Toss some weight in the trunk, sandbags, a gym bag filled with workout / free weights, and then drive around like that for another week or so.....
I would be willing to bet your springs are still simply trying to settle and find their place so to speak.
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