It's fast, that's all I care about. However, I know I get 20-21mpg highway.
I did a 320 mile trip from St Louis back to the Chicago burbs.
I thought I was getting 10mpg city, but I don't know for sure yet.
I've often had older gas in the tank and ran it so that could be one of my issues.
I have to run a fresh tank through it after this Spring to recheck that.
GTO LS1/4L60e drivetrain.