I have a Zone 6" with 35s and tow daily around 4500. I use weight distribution hitch and have zero sag in rear even with the bed of truck loaded and towing. weight distribution cost was $380 Installed. I was also considering timbren bumpstop and Airlift system. I'm sure as others have mentioned that the Airlift would work but i prefer the stability of the weight distribution hitch.
Zone 6" Lift, Toyo MT 35x12.5x20, Procomp 6033 20X9 0-offset, Inyati Spray-in Bedliner. 33% tint.