gas mileage/ rear end

[grantfire319]

Really enjoyed the site. Lots of good info. I have a question for you guys. I have a 94 K2500 ext cab, 350, KN AF, straight exhaust with flowmasters. I recently did a tune up, new plugs, wires, changed fuel filter, cleaned intake valves via sea foam, injector cleaner. Anyway... my gas mileage is still horrible. I get about 10MPG. Is that my rear end is a 4:10 (I think). ANy way to identify this ?

Also is there any site I can go to where I can build my own intake box and stuff?

Thanks.

[discostu]

Well if the gears haven't been changed, you can find your RPO codes in your glovebox. Then match it up on several websites. Google "GM RPO codes" to find some.
Gxx should be your gears (GT8 is 4.10 for example).

What size are your tires? If you are running any larger then 31", then 4.10s are pretty much necessary to maintain decent performance and acceleration.

Also, what transmission do you have? 4.10s aren't bad in a 700R4, but with a Turbo 350/400 the 4.10s will probably hurt your mileage.

[Chevyman247]

You can also find out what gear ratio you have by taking off the diff cover and looking for numbers printed on the ring gear, divide the bigger number by the smaller number to get your gear ratio.