By watching your vid, I think you could bang the shifter faster and harder. That could lower your times. I heard that getting a tune for the LFX do wonders. Lastly, your rims are killing you; there killing the SS times and 0-60, so its even worst for V6 that has less torq in a heavy car.
Congrats on cutting a full second on your time!
4th Gen SS/LS2 SB/LS3 heads/N20