I have a simple/dumb question for you guys. I am planning on taking my Titan Off-Roading around the Flagstaff, AZ area in the first week of January. I have a 2006 SE KC, big tow, and 4x4. My question is, when should I engage 4 wheel drive? There's gonna be snow up there, and I'm not sure when I should use it...Rookie question I know. lol. Thanks for your help!