I have a 01 EC 5.3 Sierra. I am looking for mods to increase power, gas mileage, and throttle response. What are some easy mods that don't cost major bucks? How much do the stock cats flow? I was thinking of going with a true dual 2.5" with an x-pipe and two Dynomax Turbo mufflers. I want something very quiet, but an increase in power. Also, I was thinking of getting a custom tune once the warranty is up. Will the 160* thermostat help out any? What about underdrive pulleys? Any intake bolt-ons that give a good power increase? Thanks a lot for any help.

 

Low cost mods:
-Remove MAF screen(free)
-Bypass Throttle body coolant line($4)
-Trim EGR(free)
-LT1 or LS1 electric fans ($100-200)
-Underdrive pulleys($200-300)
-K&N FIPK or other air intake($200-350)
-Custom Exhaust($150-300)
-Hypertech Power Programmer III ($230-300)
There are others like spark plugs and wires, etc, but these are a good start to increase throttle response for not a heavy price tag.
From what I have heard, the stock cats flow pretty good. I would keep them on.
You are on the right track with the exhaust. 2.5" for all the pipes, good flowing mufflers, and a X pipe work good on the trucks. Just don't make it too free-flowing. The trucks need backpressure for low end torque.
The Hypertech is a good start on a custom program that has a few nice benefits. Worth it IMO. The 160* stat is cool. Not a huge difference performance wise, but it does its job.
The underdrive pulley, and electric fans are great for throttle response.
You can do a search on anything listed above and should find some good info to help you decide.
Sorry so long, I was bored. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

THanks for the ideas. I will probably do the little stuff first. Then an intake and exhaust are on the way. How much power will these mods add? My truck is a dog with the 3.42s, but I don't want to go to a lower gear because of the gas mileage. I'm thinking that the custom tune will add more power than either of these, but I've got about 15,000 miles to go before I go that route. Any more info? TIA

 

With all the mods I have, I still get good gas mileage. We just got back from the Supra Shootout at River City Raceway Sunday, a 420 mile round trip for me. With my 373 gears(up from stock 342) and the mods (elec fans to now) driving 75 to 85 the whole way, I still got 18.5 mph. Doing the speed limit, 55, I ran a tank on my trips to work for aa week, I avg 19.8 mpg. Hot rodding like hell and cutouts open and closed, I avg 16.5. I guess what I am saying is , a 373 gear won't kill your mileage. I actually lost less than 1 mpg when I did the swap.