What's your budget? To get any increase on that motor you need some of these higher cost items. They are as follows; Splitport heads (99-04), gears, cam, motor swap, full exhaust, full suspension and/or turbo/supercharger. If it's not one of those or even a few of those you will see no gains on that particular motor from anything else. Personally your best bet is gears, exhaust, and suspension.
Sent from my SAMSUNG-SM-G920AZ using Mustang Evolution mobile app