To the OP, look, this is physics really, these trucks are heavy with an engine that IMHO is somewhat underpowered to begin with so yes, like you, I sought out more HP and torque. What I learned along the way is having to separate fact from fiction and marry it to reality. My truck with two dudes in it and a half-tank of gas comes in right about 5000lbs, that's ALOT of vehicle to get up and make boogie. So right there is reality, this ain't a sports car and it's not a V8, without an SC, it's not going to do 12 sec 1/4 miles. Then it's what do you want to do with that power? If the answer is to drive fast, then good luck when it comes to any sudden turns, get a sports car, you'll live longer. Me, I wanted to have enough on tap to get up to freeway speeds quickly, pass quickly and pull the occasional heavy trailer. The insurance is too fucking expensive to drive fast anyways. So after MUCH research and having run across a few bogus claims along the way, here's what I did, it's still a work in progress but so far it's made DEFINITE improvements:
MAF Calibrator, this will salvage your gas mileage after you put on a Cold Air Intake like the 63 series K&N that I put on. Be prepared to solder onto the wiring harness behind your glove box, price $212.00 shipped.
2. Cat back exhaust, three inch stainless steel, nice exhaust note, minimal gains but I think I will gain more when I put on the shorty headers and Y pipe. $800 or so.
3. Be realistic, I dropped about 1400-1500 plus the hours to put everything on and I still have a ways to go. I don't want to spin the tires and I would rarely ever need to go 110, but when I do it gets me there quicker than stock.
I will probably end up dropping around another grand+ to get the shorty headers and Y pipe bought and installed, at that point I will have gotten all of the available power out of that engine short of a SC. I put in the best plugs and change the oil every 3000K religiously with only synthetic oil. My philosophy is simple, make it as easy as possible for the engine to breathe and don't do anything that will possibly wreck it or piss off the ECU.
Bottom line my truck hauls ass for a 5000 lb, six cylinder truck. Yeah, it was worth it. To any Taco owners that don't think (therfore don't have), that the CAI and cat-back exhaust add HP and torque, I will GLADLY race you for pink slips!