The factory settings for AFR are pretty rich.
Increasing them should result in a mpg increase.
A tuned carb vs. tuned efi HWY MPG should be =
A tuned carb "" CITY MPG will be much better w/ efi due to more efficient use of fuel.
With "tuned" implying it is attempting to hit 14.7 target.
If you want even better HWY mpg increase cruise AFR.
Anything lower than 14.7 will waste fuel/decrease mpg.
Cruising I've gotten excellent results running ~15.5 AFR.
But GM TBI has a lean cruise hack