I have a 2006 Silverado with the 4.8L. I recently added a 77 series K&N intake and some long tube Pacesetter headers. I also purchased the Superchips Cortex to do some tuning on my truck and hopefully get some better gas mileage. I was running the 91 performance tune and was getting about 17 or 18 MPG. For the past week or two Ive noticed my mileage going down alot. Just filled up today and Im averaging 12.5 MPG. I went and checked the settings for my tune and I noticed we had the tires set at 30.25". I measured the tires again tonight and they were 30" so I changed the tire size in the tune settings. Would that 1/4" affect the tune that much or is it something else? I also took the 91 tune out tonight and put the MileageXS tune to see if that will help me out any? Anybody got any ideas on what could be causing this? Thanks.

 

Hi copenhagencowboy,

Welcome to the Chevy Forums.

The intake and exhaust are going to dramatically improve your flow-through, and unlock a lot of trapped horsepower, but you get all this at the cost of MPG.

Programmers are good to use for making diagnostics scans, and for changing PCM parameters,(like tire size, or a change in gear ratios) but most of us who have them have noticed a minimal improvement in power or economy from them at best.

You may want to do a thread search in this section about PCM chips. Most of the guys who've done it like it better than a hand-held programmer.