Realistically you might see a 3mpg gain. I'd expect a good mpg tune, easy driving you would be in the early 20s, maybe 25 tops. After that you need to add power adders like water/meth, or propane/CNG to see even further gains. These trucks are about 700lbs heavier than previous.
Sent from my Autoguide iPhone app
2012 Chevy 3500HD LTZ, Crew Long, Z71, EFI Live by No Limit Automotive and Performance, WCF 475 Over Stock, 5" Flo~Pro Turn Down Exhaust, Fass 150, WCF CP4 Delete, Sportsman CP3, Torque Converter, 275/70/18 M55 on Fuel Mavericks, White Line-x rocker panels, White line-x Bushwacker pocket flares, DDM Tuning HIDs 4300k, Hi/Lo Beams, Custom JetCraft sled deck, Nathan K3LA, Onboard Air Via Viair 400c/444c Compressors, Autometer Pillar, with Cobalt Boost, Pyro, Rail Pressure Gauges.