You want a cheap mod? Take a 1/4" drill bit and drill your fuel injectors out. Puts the fuel right to the motor. Haulin azz after that.
But seriously, get a programmer if you want performance. But if you want gas mileage, I use Lucas fuel additive to clean out my system. And I've done a seafoam treatment. Cleans the upper and lower parts of the engine. Pretty spiffy. But in all honestly bro, it's a jeep, gas mileage is gonna be a problem, day or night, rain or shine
Build Thread: http://www.jeepforum.com/forum/f22/500-wj-project-soon-dd-1255793