Hey JP i guess it really depends on what you use it for. If you rock crawl you don't have to have a mud terrain but can if you want, if it sees mud you need 'em i am kinda partial to bfg and super swamper and for the most part all the lines they offer are good for their intanded use. I Know you can run 31 and 32" tires with 5.5" lift and i have heard of 33 12.50 15 on there also but many guys with the 5.5" lift have a body lift to run 33's for more room for articulation. and yes i think the stock tires are too small for that lift. The oem rims are ok though. you need to go taller and wider especially if you go with any lift over 2 or 3 inches. hope this helps.
kyle