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Discussion Starter · #1 ·
I just completed a trip from Oklahoma to California and back again, and noticed some quirks in performance and MPG.

For the majority of the trip I averaged about 19-21 MPG between fillups, except for one area between NM and AZ where I averaged 22-24 MPG and my engine felt like it had gained about 10 hp?!

The weird part is that I was at 4500 to almost 6000 ft elevation. I was expecting mileage and performance to drop due to thinner air. On the trip out I thought air temp may have played a part as it was night and 75-80 degrees. But, on the way back I noticed the same gain in this area during the day at 108 - 112 degrees outside.

What gives, do I have to move to a higher altitude to get optimal performance and mileage, or can the ECM be reprogrammed?

For what its worth, I use 87 octane, and have the auto trans and 7200 miles.
 

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Discussion Starter · #3 · (Edited)
Strange, I had beeen using premium up until about 2 months ago, and noticed absolutely no change in mileage or performance at my present altitude after I changed to regular. Maybe it is just at the tipping point of where the ECU changes the mapping?

I just wish I could figure out how to make it run like that all the time. By the seat of the pants dyno, it felt like at least a 10 HP increase and revved much quicker and was way more responsive than normal.
 

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Discussion Starter · #7 · (Edited)
:bigthumb:Thank you for all the input, it makes a lot more sense now. I had also forgotten about the gas mix until Bartt and Redthunder mentioned it. Most of the filling stations out there advertised they did not add any alcohol. I did not think it would have that great of an effect, but that's what I get for thinking...:lol:
 
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