Twice a year I remove my rear liners to clean up there. There are 3 rubber plugs in both rear wheel wells, pull them out and hose the area out/spray undercoating. Dirt gets trapped between the panels and causes the rust above the rear wheels on these trucks. Usually pull my tail lights to hose out as well.
Tons of guys go off road with levels and 33s. They perform fine on the normal fire roads etc.. Probably gain close to an inch in ground clearance over stock tires, and will most likely rub the felt liner in off camber turns/bumps