Miles per gallon?

Your car has a problem. I don't care how much city driving vs. highway driving you do. It's not normal for a slant six to be getting 10-11mpg unless you're flooring it from every stop.

My guess is that you have a remanufactured carb on there. Back in the day I was getting 10mpg with a remanned carb. Put a NOS carb on and it jumped to 15-16mpg. Did other modifications and now I'm up to a consistent 20mpg in the summer and no worse than 17mpg in the winter. I do more highway driving than you, but even on the weeks that I'm in stop and go more often, it still doesn't dip down much.