Yep..., it's a big step from trail runn'n to rock crawling.
For trails.., what you have now is what you need.
For "ROCK-CRAWLING" if you mean that literally..., a fat wallet is needed & many parts/upgrades.
What Seabronc is showing is a good start..., & a good price. However, I don't know if
rock crawling
with a FSB is the way to go...?
If you're just look'n for lower gears for some up-n-down hills-n-trails with exposed rocks, etc., meaning
you want to change the "
axle gear ratio" only via the pumpkin ring-n-pinion..., that's doable.
However.., not cheap either. You likely have 350's front-n-rear now. Going to 411's would give you
lower gearing/low rpm torque.
Having said that.., I too have no first hand experience "rock crawling" or building one.
Heavy damage is always part of that game.
There may be some folks on this site that "crawl" with their EB's. We'll see if they chime in...