svt injectors pump and maf will not help you. you want to decrease fuel economy, not increase your fuel throughput.
the best way to help you would be to continue your tune up.
o2 sensor, pcv valve, check egr. also those big wheels in your avatar wouldnt help either.
spending alot of money on a tune and intake etc, will liekly take forever to pay that back with gas savings (assuming they even save you gas). the only thing that might help is small, light wheels with LRR tires.
for auto-x: '04 Liquid Grey ZX3
for street: '02 Infrared SVT