Hi Folks. I have a 2006 GMC 2500HD with a LBZ and 90,000 on the clock. I bought it last October. I am running a bully dog triple dog downloader on the Tow/Economy Tune. Other than that the truck is stock. The oil is about 2,000 miles old. New air and fuel filter last week. Tires size and pressure at GMC specs. The only problem is a check engine light for a bad glow plug i have to fix before winter. I was getting about 16 city and 21 highway with the truck. About a month a go i started noticing it was slowly using more fuel, and i calculated it to be getting about 13 city, 16 highway. Why would this be? Any Ideas?

First you have to carefully think if you have changed anything. Runnng the A/C more, changed tires, buy fuel from a different place or are driving completely different roads. From there ditch the tuner for a few tankfuls. Mine has dropped lately myself. I won't panic yet though. I towed thru a huge rain storm heading right into the wind the whole way. Following tank I had B5 in it. I'll tow again on Labor day and if I get back to 12+ towing then I will attribute my loss to those other circumstances.

^ what he said.

Also "performance" usually gets the best mileage

EGR may be going bad.

About the egr valve, can i just put in a blocker plate and fingerstick? How will that effect my mileage ?

About the egr valve, can i just put in a blocker plate and fingerstick? How will that effect my mileage ?


I am not positive, but I think yes you can. I think you would still need to clear the fault code too. The "finger stick" is supposed to simulate a "good" value and fool the ecm. The blocker plate would plug up the leak from the EGR. I still need to do this to my truck.

My egr is not throwing any codes i was just taking the suggestion that it was going bad. I ordered a blocker plate. The egr doesnt need to be working right for the plate to function right?