Looking for a little more power without adversly affecting MPG's.....

Hello I have a 2005 Avalanche Z71 5.3L/4L60E 3.42 gears with 265/70/17 at's and right now I'm avging 18.8 mpg's and yesterday we had a medical emergency and i kept slambing against the 98mph speed limiter so I decided right then and there that when I got home that I was going to rid myself of that problem... Well now that I've used up one of my tuning license on that I may as well all a few goodies in the mix, however I'm looking for items that'll give me a few more ponys while making this thing funner to drive and without hurting my mpg's whenever I keep the cruise control on (that's the only way I can get 18.8 mpgs because i was born with a heavy foot....LOL) I've been looking at those ebay CAI's and billet MAF housings and been looking at various 3" in/out mufflers, anyone have any proven results from any particular cai', muffler and custom tunes? The ideal thing would be if i can could get a few more ponys and a a few more mpg's along with it but I know that's a hard balancing act.