First off, I'd strongly suggest everyone stick with Monroe Sensatrac shocks. They are 'rated' the same as KYB and are cheaper, while retaining the ELC function.
The rear suspension is dependent not only on the springs and the ELC (for those equipped, but also on the shock itself. These are NOT AIR SHOCKS. These are GAS shocks with AIR assist.
So the air can leak, and the gas be fine, or the other way around. Keep in mind this is for the next gen, but it'* a great guide:
If your *** doesn't drag (ELC works) but the ride is still too soft, your gas portion of the rear shocks are likely shot. ELC adds alot to feel and cornering performance. This makes the Sensatrac'* with ELC retained a much more viable alternative to the KYB.