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I installed KYB's twelve years ago. They are still on there and I see no reason to change them. I would buy them again.
I'd pull them out and compare them with a known good shock. BTDT with shocks that felt as good as day 1. Problem is that the shocks go bad SLOWLY so it is hard to know what to feel. I'd push both down and see how well they come up. You might be surprised at what you see. If it is good, return the shock to whatever parts store you got them from. If it is bad, buy another.
In my opinion KYB's are decent shock absorbers. I have used them many times and never had any troubles with the units I installed. I had them on my C3 and on German sports cars as well. They are not the "softest" if that is what you are looking for but they won't jar the fillings out of your teeth over a rough road either.
Bilstien Shocks work very well but you will feel every bump on the road. They are just a bit too stiff for my liking.
Cheap shocks belong on cheap cars....
I wish you all a Very Merry Christmas and an awesome New Year for enjoying your Corvette!