Improving MPG

Your 3.23 and factory torque converter are probably best for your scenario of city and high way driving and getting decent mileage.

I agree with 805's detailed check list. Get all that done first then start thinking about the next step after you have optimized your existing setup.

Maybe if it were I and I wanted a daily driver with a bit of balls but fuel efficient, I would get an after market mild TBI setup and ditch the questionable carb.

Other than simply and cheaply doing what 805 and others suggested about optimizing your existing system, there is really no way to get ROI on expensive mods designed to make better fuel mileage unless your car some how magically transforms to 35 MPG or you are going to drive that vehicle which may end up at a realistic 22 mpg best case scenario, for a quarter million miles. Then you may see ROI on complex mods. But the fantastic benefits of engine longevity and ease of drivability combined with a bit better mileage may be worth switching to an econo TBI.

https://www.affordable-fuel-injection.com/

http://hamiltonfuelinjection.com/category/2-tbi-throttle-body-injection.aspx

Buy an economical daily driver like a 96 2wd 4 cylinder 5 speed ranger or a geo metro 5 speed if you want excellent mileage.