Hypertech for Gas Mileage?

I'm an old gear head and I've haven't done much with these new computer controled motors. In years past I would pull the vacuum off of the secondaries to save fuel and up the mileage. I have a 02 Silverado HD 4x4 Crew with the 6.0 and 4speed auto and 3:73 rear. I'm getting 12 to 14 mpg around town and 15 highway. I was wondering if you could use a Hypertech programer to help your gas mileage? A buddy of mine has a Durango and he uses a programer on it for gas mileage, he sets it for mileage and then when he needs to tow he resets it for performance. When he's not towing he gets 18 to 19 and when he tows it's 15. Has anyone done this? The performace of the truck is great, so if I could tune it down for daily use it would still be fine and then turn it up again when I need to tow.. I'd like to put a couple of bucks back in my pocket on the fuel side of things.

I've got an 01 hd 4x4 and it didn't help mileage very much. maybe 1/2 to 1 mpg. I am looking at someone to flash my computer with a custome tune. www.westersgarage.com. I've heard great things about them on gm-trucks.com.

I have one in my 1999 3/4 ton P/U and its great. Get about a mile or two more if you stay off the gas pedal, but then I tow a 16x 8 foot car trailer with buggy and bikes, and get about 15mpg. I also put a peice of plywood to deflect the wind over the tailgate, and with no load I get about 17 on the highway. A more open exhaust would help also.