the rear will never keep up with anything you do to the front unless you link it.
Here's a video of my truck, on 40s with a blown rear shock going through the whoops. The front suspension is dialed and money ( its an svc mid-travel kit).
you can see that until the rear is sorted and tuned ( and even then it will be what holds you back), you arent going to go any faster through big stuff, as the rear of the truck will be flopping around and make it so you cant go any faster.
If you carry supplies/weight in the bed regularly, I'd do leafs, a bump kit and shocks. Then I'd have someone tune the rear shocks.
As your budget permits, start changing out what is holding the front back.
My truck cycles about 17.5" in the front and 22-23" in the rear. It is still leaf sprung. Traction bars are a godsend.