How to Increase gas mileage on 2011 2500HD Duramax 6.6?

As you mentioned that your GM 2500HD is of year 2011,this clears that its newest model ans under full warranty.If your vehicle is under warranty,then doing this on your own will void the warranty.To be honest their is not much you can do. On newer model vehicles every thing is controlled by programming chips.Since the chips and programmers get the best results they are recommended but they leave footprints that may impact warranty.
So the things you can do are change to a cold air intake, and maybe modify the exhaust slightly but even that is hard.
One trick is to get a second PCM and program it with the chip. Then if you do need warranty you switch the PCM out and the footprints are gone.

There are some companies which sell GF Performance Chip online.Also they claim,that warranty of your vehicle will not void.But they don't provide any kind of guarantee.But yes this GF Performance Chip are genuine in most cases.But still confirm before buying.

This details will help.Thanks.

--------------

See below list of solved fuel related car problems :----------

How to maximize fuel economy on your vehicle?

http://schematicsdiagram.blogspot.com/2011/11/how-to-maximize-fuel-economy-on-your.html

For more Fuel/gasoline related help, follow the list mentioned below: -----

Fuel pump relay and cooling fan relay troubleshooting on 1997 ford thunderbird?

http://repairhelpcenter.blogspot.com/2011/10/fuel-pump-relay-and-cooling-fan-relay.html

How to Test and Replace Fuel Injectors on Acura Car Models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-fuel-injectors.html

How to replace Fuel Tank Assembly?

http://vwrepairhelp.blogspot.com/2011/11/how-to-replace-fuel-tank-assembly.html

FUEL LINES AND FITTINGS on Acura Car Models?

http://repairhelpcenter.blogspot.com/2011/11/fuel-lines-and-fittings-on-acura-car.html

Replacing Fuel Charging Assembly on Car?

http://vwrepairhelp.blogspot.com/2011/11/replacing-fuel-charging-assembly-on-car.html

How to replace Fuel Pressure Regulator on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-fuel-pressure-regulator.html

How to test Fuel Pressure and replace Fuel Pump on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-fuel-pressure-and-replace.html

PGM-FI Main Relay on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/pgm-fi-main-relay-on-acura-car-models.html

How to Relieve Fuel System Pressure on Acura Car Models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-relieve-fuel-system-pressure-on.html

How to Replace a Fuel Injector

http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-injector.html

How to Replace a Fuel Pressure Regulator?

http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-pressure-regulator.html

How to Replace a Fuel Pump?

http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-pump.html

HOW TO CLEAN A FUEL SYSTEM

http://schematicsdiagram.blogspot.com/2011/07/how-to-clean-fuel-system.html

HOW TO REPLACE A FUEL TANK

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-fuel-tank.html

 

HOW TO REPLACE A FUEL TANK CAP

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-fuel-tank-cap.html

HOW TO REPLACE A FUEL PUMP ASSEMBLY

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-fuel-pump-assembly.html

Time to replace Fuel pump on 1998 Ford Explorer?

http://schematicsdiagram.blogspot.com/2011/12/time-to-replace-fuel-pump-on-1998-ford.html

Emergency fuel shut switch on Ford car?

http://schematicsdiagram.blogspot.com/2011/12/emergency-fuel-shut-switch-on-ford-car.html

How to jump fuel pump On Chevrolet Silverado 1500?

http://schematicsdiagram.blogspot.com/2011/12/how-to-jump-fuel-pump-on-chevrolet.html

Car won’t start when cold?

http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-when-cold.html

Car won't start after sitting overnight?

http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-after-sitting-overnight.html

Car loses power while acceleration?

http://schematicsdiagram.blogspot.com/2011/12/car-loses-power-while-acceleration.html