I think for someone who hasn't tried it before I'd start out trying 5th to 6th. To me that is by far the easiest change.
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05 QC, 4x4, Short Bed, SB 3600 DD, NV56, 35/12.5/17, 2" leveling kit, Amsoil 6080, Pusher, 5" TBE, boost fooler, TNT setting 3, Dipricol Pyro, Boost, & Fuel Press, HID's, Cobra 29 WX NW ST
http://www.youtube.com/watch?v=ZK78fZt2w8E