Technically a good intake and exhaust will help out your MPG but you have to watch out. When your truck makes more noise, your going to want to hear it, which leads to a much heavier right foot in the beginning. At least that's how it is for me.:great:
But anyways yes they will help. K&N,S&B,Airaid and others make some pretty decent intakes. Flowmaster exhaust which in my opionion sound the best, haven't really yielded me any good mpg or hp numbers. Now magnaflow, borla, corsa and gibson will give you a little of both.
Another route you might consider is a programmer/tuner. Hypertech, Jet and Superchips all make good one's and you'll probly see the most benefit from one of those. The more things you do the better. Hope this helps.