Hi, I bought an 99 chevy 1/2 ton z71 5.3 ec,sb. It has ss bumpers, door handles, 22'' rims. Whats the bigest improvements to do to it? K&N intake? chip? Just looking to improve gas milage and power?

I had a 99. put on dual exhaust and a hypertech. Didn't notice any performance differance, but sure sounded nice. Ended up going with a 40 series flowmaster, with single 3" in and dual 2.5" outs. A buddy of mine has a 99 with a 4.8, he put on a CAI and didn't notice any performance or mileage improvements.

try a whipple super charger.got one on my 2000 yukon xl holy....

I put a drop-in K&N in my 2000 4.8L and noticed no difference in performance or mpg. Don't know that a CAI would be much better as the Vortec breathes pretty good stock. What made the best improvement for me was a single outlet Flowmaster 40 necked down from the stock 2.75" to 2.5". It gave the truck a lot more low end punch. It may have sacrificed a little on the top end, but I rarely took the needle over 3500 rpm in 135,000 miles.

I have a 5.3 and I have had a 4.8, and I did the exact same mods to both of them. I took the air box and removed that piece that connects it with the fender. That made the hole double in size. I then took the screen out of the mass air flow. (be careful doing that) and unhooked the battery. That made the most difference, and didn't cost a dime.
I also put true duals on the exhaust. I split the pipe right were the two pipes come together. I ran 2.5 inch pipe to two Dynomax Super Turbo's with 2.5 inch interternal tubing. I also put an H pipe in there as well. Then, since the both banks of cylinders have to run down the passenger side, I figured that I should switch the tail pipes, meaning that the passenger bank of cylinders exited out of the drivers side of the truck and vice versa. That would equal the length of pipe because the drivers tailpipe had to go back across to that side from the passenger making it much longer than the passenger side. So, I basically have equal length pipe with an H for good measure. Sounds really good, but can't say that I picked up much from it. I think to unlock this setups potential, I need a tune.

A cam will give you the most bang for the buck, and there really not that hard to put in these motors. I took my time and did a cam and valve springs in about 8-9 hours.

Programmers & exhaust improvements seem to make them run better but haven't been able to prove any mileage gains.

My brother has one like yours and he improved his mileage by going to a 4.10 rear and a PCM tune (87 octane). But it depends on the type of driving you do though.
JP

pull it and drop in an 8.1 jk

STS turbo kits are supposed to be amazing, but I have not been able to spring for the $5,000 to get one yet. I tried a JBA exhaust on mine but it made no difference and the drone was annoying. Corsa is supposedly the only "drone free" exhaust for these engines.

STS turbo kits are supposed to be amazing, but I have not been able to spring for the $5,000 to get one yet. I tried a JBA exhaust on mine but it made no difference and the drone was annoying. Corsa is supposedly the only "drone free" exhaust for these engines.

Yes, STS kits are quite nice! ;)

trade it for a DMAX!!!