Dual rear shocks??

[vtblazer]

I changed from 1/2 ton springs to 3/4 ton springs on the rear of a 2wd truck one time and found it mandatory to change out the brand new 1/2 ton shocks due to the fact they couldn't control the higher rebound rate produced by the heavier spring pressure.
Installed a shock rated for the purpose and the problem was solved.

Not really a direct comparison to your issue but IMO, it's all about the valving of the shock your running.