Does your truck have rpo code ZW7? The self leveling shocks on the back? You can't replace those with regular shocks, as the spring design can not support the weight. I know you are more specifically addressing the front end, just wanted to put it out there.
If you adjusted your new shocks out for 2" of lift it should be 10x better. The only other thing that I can think of is you need to come off on your adjustment bolts a few turns. You don't want the torsion bar keys to be maxed-out in any instance. A little over halfway is the sweet spot from what I've found.
Have you had the wheels re-aligned yet? The control arms and sway bar links should all be loosened when you drop the suspension down. If you skipped that step then the alignment would also help when the tech goes to loosen-up all the pivot points and allows the CA bushings out of their bind. I hate that you didn't end up with a noticeable improvement regarding ride quality. The bump stop extensions will help with overall handling but it's not going to soften it up or improve the rebound.
