Please will you explain to me how your airbags keep you at 4" all the time H?I like the air bag idea. Keeps you at ~4" all the time, no matter what the load. Then you can set the driveshaft pinion angles dead on for 4" and minimize the vibes.
The bumpstop extensions may be a bit too long. Try some high dollar offroad shocks that maximize suspension travel, making sure they ride in the sweet spot for 4".