I own a bridge in New York that I will sell you for real cheap.....
There are hand-held units that you simply plug into the diagnostic port under the dash, upload the program and Voila!, 60hp. The 7 mpg is a lie! Some folks have claimed .5-1.5 mpg but anything much over that I would be very skeptical.
There are also software packages that you can buy to load to your laptop and create your own ECM programs called "tunes". The software allows you to adjust fuel pressure, pulse width, etc. to customize it to your particular needs....it ain't that easy and it's not cheap.
With both of these types of upgrades 60hp is on the low end of what is possible. Some tuners can load upwards of 200+ hp and 100s of ft lbs of torque to your truck. Go out to Google and type in Duramax Tuners and start your research. Good luck.
Jeff
"But officer, I ain't Speedin', I'm just flyin' low"
2001 Silverado 3500 Dually LS Ext Cab, 6.6L Diesel, Banks Stinger Kit, 4" Exhaust, VR Straps, Bilstein shocks, 255/85/16 BFG KM2s
2004 Suburban 2500 LT 6.0L 4x4, Bilstein Shocks, Federico front/rear sway bars
1996 Caprice 5.7L LT1, B4U Suspension, KYB shocks & Hotchkis sway bars, BMR RCA - alas I miss ya.
2013 Caprice PPV 6.0L