I have an '04 Buick Rainier with the 5.3 V8 that is completely factory and I am fairly happy with the gas mileage I am currently getting.

With that being said, what are some easy modifications I can make to increase the performance and possibly gas mileage?

There a decent cold air intake you guys would recommend?

Anything else? We have good tires on there (Michelin) and properly aired up.

Been rearching on other boards, leaning towards a Volant CAI and PCMforLess tune.

Any other thoughts?

Just curious, but what is a tuned PCM going to do for fuel mileage?

From Bryan at PCMforLess:

"On the Rainier'* with the 5.3 I can pick you up 15HP on 87 octane and 20 to 25 if you run premium. I can also firm up your shifts, improve the shift points, move up the top speed limiter and improve part throttle response and mileage (typically .5 to 1.5 MPG)
You can also do little things like cold air intakes and exhaust for added power and economy as well."

Let me know what you think about what he has to say.

With today'* gas prices, and the need to increase your MPG, running premium is rhetorical.

Firming up the shifts only means the shifts happen quicker. This might help MPG.

Leave the speed limiter alone. If your ever given a speeding ticket for 130 and there was a Porshe next to you, you could prove that your vehicle wasn't going that fast because you are stuck at the factory speed limiter.

CAI would help.

Thanks for the info. That response was to when I asked what could they do for my vehicle.

I had no intentions on changing the speed limiter....this is a daily driver. I just figured if it would help a little and get some more performance why not give it a whirl but really wanted some more advice / suggestions before doing so.

You could upgrade the exhaust. You might get a slight bump in power, as well as a small increase in mileage. Also, you should make sure all maintenance is up to date, like plugs, wires, air and fuel filters, transmission fluid, engine oil, etc. Don't forget to make sure your tires are properly inflated too.

With all that said.. the best way to get max fuel economy is to adjust your driving style. There are so many small bad habits that reduce gas mileage. When I drive to my parents' (about 400km), when I don't use cruise control, I average about 25mpg..but when I use the cruise control, and take my time, I can get almost 35mpg.