depending on where you are at geographically, the EPA 'winter fuel' program my be the gremlin you're searching for..

if you're using 93 on the 93 tune, and wondering why it gets better mileage? because there is a massive difference between 87/9 and 93 in winter blends.. I would venture a guess that the 87/9 blend is butane and ethanol laden and runs through your engine like a glass of Mumbai water does through a 'good ol boy'.. (Mumbai sh&^ pie, if you've never experienced it, just simply take my word for it)

I'm going to throw this out there just for thinking purpose- but it's my firm opinion that you DON'T want to 'experiment' with fuels and tunes in the middle of 'winter blend' season.. run what runs perceptively better, and let it go.. in April~June, the EPA mandates the shift to 'summer blends', and those blends are better for performance as well as 'making engines happy'.. THAT is when you'll want to experiment.. the butane content decreases significantly, and you'll often find that 87/9 runs almost as good as 91 to 93 does in the winter..

 

I assume you looked ALL around inside the intake with a mirror and flashlight? Mine gasket was blown at 78K. And get a PCV valve from the dealer.

 

I agree, plus, the colder temps means cooler air= IAT and a cooler running motor= ECT. Which in turn tell the PCM to dump in more fuel. Last time I checked and posted my MPG's it was a hair over 14, I just checked it the other day and I'm down to 12. Same Rt. , driving habits and same gas station.

 

yes, the inside was spotless except for a small pattern coming from the pcv.

I'm in Pa., most gas here has 10% ethanol.

Should both 02's be changed? I thought only the front one controlled mpg?

 

Change both 02's, they both play a roll in fuel trim.

 

Just for comparison, I've got the same truck except I have the 5.2 and am also in PA. I get 12.5 to 13.5 on 89 octane with no tuner. This is driving rather sedately to and from work much somewhat worse when I run it a little harder tow anything. On the other hand I have an 05 QC with the 5.7 hemi and get 14.5 to 16+ and a LOT better performance.

 

I usually get closer to 12.5. Mine has 3.55 gears. You said you were getting 11.5 going off the computer, which you stated wasn't all that accurate. I think you also said you had an offroad edition, which probably has 4.10 gears. Your gas mileage may be normal.

 

I have a 5.9 4x4 with 3.92 gears. I get average around 9 mpg driving slower than a kalamazzo(for those of you that watched comfy couch). Check your cat and o2 sensors those are the major culprits.