I have a 2003 Chevy 1500 ext cab Z71 with 5.3 liter and automatic transmission. I have a K&N cold air intake and dual 2.5" exhaust from the cat back. Is there anything else I can do to get better gas mileage?

 

Put x-pipe on your exhaust...if its true dual. Get electric fans from a 05+ silverado and radiator, and get a tune from blackbearperformance.com or gowheatley.com

I saw like 3mpg from the tune with these same mods. And drivin style has a lot to do with it

 

If you want your truck to be really loud and get better fuel economy you can get the cats cut off and just a pipe welded on. I thought it would give me worse fuel economy with the 02 sensors but with the better flow it gives me better fuel economy. So thats an options but if you do just be ready for your truck to be a hell of a lot louder.

 

How much did you mpg's go up?

 

Throttle body spacer- I saw 2mpg increase on my 08 Silverado.
Airaid 200-512-1 Mat, direct fit Throttle Body Spacer | Auto Parts Warehouse

 

wouldnt that make it worse.? more air in means the fuel in has to go up also to keep the right ratio

 

throttle body spacers haven't helped on a GM truck since 98...the 99 and up newer body styles don't receive any benefit from the throttle body spacer. I had one, made a cool whistle noise but that's about it

 

That would be illegal in the USA.

You could redo the exhaust to include headers, better flowing y-pipe and performance cat, but not sure if that would be worth the money. Maybe just a performance cat, but this is still illegal if you have a functioining cat.

Switch to synthetic oil, transmission/transfer case fluid and gear lube. Keep proper inflation on tires.

 

I agree with slw210. Synthetic Oils are a simple solution but do not make a huge improvement in MPG.
The cat removal is an expensive mistake.
All the performance parts will be expensive. You would have to get a lot better MPG to pay that off. If you have a low gear ratio 3.73 -410 for example, a switch to taller gears, 3.07 0r 2.73 would help a lot for MPG on the highway but kills some performance.
Try to coast more to stops and accelerate slower.
I try to do this and it helps some. My Z71 gets 15MPG in combined driving with the most miles on the highway at speeds over 70 MPG.
The new eco cars turn off their engines automatically at stoplights. (Chevy Hybrid too).

 

3.07 would kill you at starts though. right.? but alot less rpm's at higher speed.? gears confuse me, so im trying to learn a lil