I have 305/55/20 Toyo AT2s on KMC Addicts and couldn't be happier with them. Mine rub a little in the back of the driver side wheel well but my bars aren't all the way up.
Edit: Depending on what you do with the truck 285/55s are also a good option. I noticed a small drop in mileage and a little drop in quickness when I switched from 285-305(not big deals but if you tow all the time its worth noting)