I have added ez flex equalizers to my leaf springs on the th'er and shocks. that along with my air ride fifth hitch not a an air ride pin box. the pin box would be an alright idea and if your going to go that route make sure you get the tri glide by tail air. before you spend that much money on the new pin box find out how many other frames it will fit because most of the time they only fit 1 or 2 and if you get rid of yours for any reason well that's money you don't get back. if you spend the money on an air ride fifth hitch it stays in the truck and most likely the last fifth hitch you'll ever buy. imo the omni by air safe is the best and $2400 but still the best. I have the air ride .com hitch and really like it. how ever found it 1 year old used for $1300 so that was the determining factor for myself. http://air-hitch.com/
my tv is an 99 f350 drw 4x4 but my th is not as heavy as the rest of yours. it's only 10k. a friend of mine is pushing 14k loaded and he did finally add air bags to the suspension but that truck has pulled fifth's for ove 80k miles so the leafs are probably a little weak already lol
imo i pre fer the kyb mono max tow shocks. they do make the ride a bit stiffer empty but are impressive. far better than manroe or bilstein imo. if you really want the best ride order a set of fox emulsion shocks with remote resivoirs and then re-valve them until you get the ride you want. i have re-built and tuned many many of them for off road racing and it's not hard to do.