This is kind of a long post, but I have done a few different things and I want to go through them all.
I have a 99 2-door 4wd LT and have made the following mods:
Hypertech power programmer $350
160 degree stat $50 - $70
Gibson headers $400
Flowmaster 70 series muffler $350 with custom pipes
K&N cold air intake $250
For Looks I have chrome nerf bars and Scorpio Weld wheels and Pirelli Scorpion ST tyers
First the hypertech
Being a tech person I love being able to interface with my computer. You can advance the spark with the Power tuning option which requires 91 octane.
I like this. I tried removing the programming last month and had to put it back on. When you punch it with out the programming the truck kind of bogs down a bit (my truck any way) and with the good gas and the spark advance it gets right on it.
Next you can optimize for the 160 degree stat
This is good, love the fact that my truck runs cooler. Not that good in the winter though. Windshield wont defrost as well.
Shift firmness
Again this is a noticeable difference where the clutch lets out quicker and firmer. I would imagine that this would reduce ware on the clutch.
Higher RPMs
I have this setting engaged but don't think that much of it.
The other features let you change the tier size and adjust for different gears.
It also lets you raise your top speed to 126 MPH (I think)
So all in all I really like my programmer.
The headers did not make a huge difference, though they do look cool. They did bolt right on pretty easy. It did make one of the spark plugs hard to get at. I still have the stock down pipe which may be restricting the air flow. Maybe that’s why.
The K&N cold air intake did make a good difference. This really made the meaty sound come out of the engine. Also it makes this really cool hissing sound when you let off the gas. There was a noticeable change in performance as well. There is a loud vibration from 3000 – 3300 rpm’s that the stock intake cancels out with that big empty box thing that says Vortec on it.
The muffler did not make a noticeable difference. Again, this might be due to the fact that my stock down pipe is restricting my system (it does have a nasty bend) and any upgrade may not be realized until that is replaced. The 70 series is the quietest muffler that Flowmaster made when I bought it, and it does sound good. Again, as I said before the cold air intake made the biggest difference in sound.
So I did all the mods except the muffler. They were all pretty easy and I am glad I did them all. The headers were my only performance regret, but they do look cool, and show that you care (also weigh about 30 lbs or so less.
I did get vented and slotted front rotors and love them $190 for the pair.
I have not and probably will not ever dyno my truck but I would say that I am getting about 270 – 280 Hp and 350 – 370 Torq, I’m guessing who knows, but I can beat regular Tahoe’s off the line. Plus it sounds great.
Good luck.