96 Firebird Formula upgrades

Right now I am driving a 1996 Pontiac Firebird Formula Coupe. It has the WS6 package but no ram air. A few weeks ago I put it on the dyno and got about 317-321 hp. I am looking for ways to increas gas mileage as well as HorsePower. Modifications include performance pulleys/belts,K&N intake, Flowmaster exhaust system and various other small tweaks. Any suggestions would be greatly apreciated on how to increase my gas mileage. As of now I am getting roughly 13-15 city and 20-22 highway.  

Hey i know this is an olp post but if you still the formula just write back and hopefully you got some stuff under the hood already. I have a 96 formula as well but im about to sell mine so i know some mods that might help you. All my mods were mainly exhaust, ram air, some tweaks, and good driving skills and got me to 4 consecutive 13.5's in the quarter mile. I will miss my baby but plan to get one in the future. maybe and ls1 firhawk. reply if you are still interested.  

the best thing you can do is computer upgrades. jet performance, hyperteck, etc. putting a taller gear in the rearend will help with city driving. the pullies will help some not much. they mostly free up hp thats already there. you K+N and flow master will do more hurt then help gas mileage, but helps a lot with the computer programer. switching over to full synthetics (oil, trans, rearend) will work as well. royal purple works the best I think. If you have a auto trans put in a shift kit, nothing rad. you just want to cleen up how the trans works, making it more efficant.

thats about it. unless you want to go a little wild and start replacing rotating part with aluminum.

good luck. let me know what you think.