howdy fellow fiero owner. ive got one hell of a setup to try and get some FE out of, but it is a pretty efficient motor i used in my motorswap. are you a member of PFF?
a headsup, its not carb'd. thats the TBI (throttle body injectrion) system all the iron dukes in fieros have. you could aways get a MPGuino for your car like i have for mine. but if your wanting to do it the cheapest way possible, the vac. gauge would be your best bet.
45 mpg?? holy hell, thats pretty good. the epa is like 38 on that year of duke for the highway. have fun, and take good care of that car. dont junk it, restore it!
EDIT: ah yes, i have been found! (my MPGuino post on PFF) you can find a lot of info from the fiero forum.