The us model 3.1 chevy engine will give you 25 miles to the gallon.
This is a sea level average, the higher you are the better you engine will run,,,,,that is if you paid for your full at sea level.
Don't beleive me check it out,,,
fill up at 500 feet and run you car or van up to 2500 or 3000 and feel the engine it is responding better.
Now im no hero but it may be the computer is making the motor run better ,,,