Metro gas mileage

1991 Geo Metro lsi convert, 51K, 3 cyl.

I meant to ask this question as well.

My Metro consistantly get 32 mpg. It is supposed to get 40mpg for an automatic.(45-50mpg for a standard).

What can I do to increase the gas mileage?
I did a tune up myself. Replaced rotor, cap, plugs, wires, fuel filter.
Are the injectors clogged?
A friend told me about a fuel additive in a gold can (bx44?) That mechanics use. It is better than the otc stuff at Adap or Autozone.
What do you suggest?
What about the timing belt? Would a mechanic just check that to make sure it is properly timed?
Also, I can't find where the pcv filter is.

Thank you