if you want it to flex better you need to get under there and start IDing whats holding it back. the biggest culprit has always been the rear shock mounting. next is the front mounting. remove your shocks and flex it out. if you get more and im pretty sure you will, then you know you need to rework the mounts. this goes for both length and also shock-eye orientation. shocks should be mounted with the eye-bolt perpendicular to the axle housing. the stock parallel mount will cause binding. make sure the clamps on the spring packs are not clamped tight. bend them up. make sure your shackles are working right at factory torque specs. 45lbs. is incorrect. that was made up years ago and people keep passing that around. the mounts have different specs front to rear. if you torque them to specs and they bind then you need to rework them not simply leave them loose. this will grind through the bolts. make sure your shackles arent vertical. they should have some angle. i liked mine a bit exaggerated. SUA with springs that are arched aggressively naturally dont droop as well as flat springs. when a spring droops it makes an arch but if your spring already has a good amount of curve then there is no where for the spring to go and it will have less droop potential. make sure your ebrake line isnt holding you back. mine was almost taught at ride hight. the flex game is won through little battles. theres no one big thing that will totally unlock the suspension. all the little things you do will add up.
-insert meaningless out-of-place political diatribe-