You've pretty much done everything that can be done relatively "cheaply". To get additional gains you're going to have to spend a few more bucks...Some options could be:
Intake manifold/Fuel Injector Upgrades
Ignition System (MSD, etc, etc)
Regearing (3.73 and up)
Headers
Accessory Elimination/Electric Upgrade (Air Pump, AC, Water Pump, Fan)
There's really no easy, cheap answer to get more power..If you want big gains, you need to have some money. If you're willing to go without AC and have no emissions requirements in your state, then you can eliminate some of the drag on your engine by getting rid of those and possible moving to an electric pump and fan. Also, the more air you can move in and the more exhaust you can move out are generally good ways to gain some power.