ok i have a 99 ford f150 xlt supercab 4.2 l engine and have been making some mods to it. i replaced the OEM spark plugs with some with some e3 spark plugs and i replaced the spark plug wires with some aftermarket wires. i put a k and n air filter kit on the truck. i also put a body kit and some 20 inch rims with 275/45/20 tires. i realize that the diameter is close to the same as the factor rims and tires but it still feels slow. is this because of the weight of the rims? do i need to go up in gear ratio and if so what should i go up to? if the diameter is the same, what will happen if i increase the gear ratio? what other mods can i make to the 4.2l engine? and last but not least where can i possibly take my truck to find out what kind of increase in HP and torque i have made with my mods on my truck? anyone with any advice what so ever please help! not very savvy with all of this but doing as much research as can be aloud. i am in the military so i dont have all the time in the world. thanks