LBZ Tune and loss in MPG?

[FBJR]

First post...................

Anyway I have a 2006 GMC/CC/SB with the LBZ option. Love the power and did the mileage. Truck is just torsion raised to run 295's and blocks out back to level it out with Bilstein 5100 shocks. Cat back MPRP 4 in SS exhaust.

Have the 7186 tuner and have a couple questions and issues now.

Mileage was really good when I first got the truck getting about 17-18 normally with up to 21 on the freeway. This was with mid hp tune, I think 45. This was in late 2006.

One thing I did have issues with was programming for tires sizes. If I put in the correct tire Dia the truck drove like crap. ABS kicked in on any stop and the speedo was way off. I had to use the tire size and adust to around the 305 size to get the speedo right. Verified it with a radar gun and GPS. DIC was dead on with mileage and fuel used.

Late last year I upgraded to the new software on the Predator and my mileage has not been the same since. I am lucky now even driving like and old lady to get 16 around town and barely 18 on the freeway. Still the same issue with tire size with Dia so I am running it with the 295/17 size and the speedo is 2-3 MPH over at 70 MPH.

The only other change was to add the SS pipe from the downpipe to the Cat Back for better flow and put in an AirAid Air filter, just the filter, no CAI.

I towed an empty enclosed trailer (2500 lbs) for 600 miles and barely got 13 mpg going 65 with a very light foot!!!

Yes, I returned to stock tuning before I did the upgrade.

Yes, I have tried several diff tunes since then and milage will not go up.

I change oil at 3K miles and have changed the Fuel Filter too.

I always fill the tank from well used stations.

I also notice the Manual shifting does not work with the tuning in place, is this normal?

Power is great as is drivability

I now have a little over 10K miles on the truck and want my mileage back!!

FB

[johan]

The revision update did nothing with the tunes, they are identical to the prior one, we just fixed a tire size issue.
I personally change my fuel filter with every oil change.
To me it sounds like the increase in tire size is causing your drop in mileage which is quite normal.
The manual shifting should not be affected by the tune as it is in the allison TCM and we do not touch that.
I also know of an EGR issue that happened on many of the 06 LBZ trucks, it could be something with that as well that could cause a drop in your mileage.
I personally think it is most likely the tires, rotational mass increases has a huge impact on mileage.

[FBJR]

The tires are the same. I put them on when I bought the truck in mid 06. All that has changed is the tuner update and air filter.

I hope it is the EGR as I have a blocker for that. Will the tuner over ride the EGR code setting or just reset it?

thx

[johan]

Yeah an air filter would not cause a decrease in mileage.
Right now the tuner will not over ride the egr codes, I have not found anyone to test it out, if you are willing we could try some custom tunes once you get the blocker plate on there to eliminate the codes. If it works i would add it in as a custom parameter.

[FBJR]

Great, I would be willing to try it for sure. I replied the same in the other post REF the EGR codes.