i have a 02 silverado 2500 hd crew cab with the 8.1 vortex thats getting 6-8 miles to the gallon does anyone know if a performance chip would increase the gpm and if so which would be the best for that particular motor.what would be the draw backs to installing one.

 

WOW, 6 mpg? that is horrible. Even for the 8.1 I would think there is something wrong with it. Do you have lift, bigger tires or something?

That's getting down to semi-truck mileage.

 

Performance 'chips' usually aren't either, the ones you'll find sub 200$ range are fake, period.

 

You're posting this in the wrong forum. You should move it to the GM forum for better response.

Sounds like you have something else going on (unless it was always like that), so the chip probably wouldn't help much. I'd find out what the problem is first.
Fuel filter, air filter, plugs, wires, MAF sensor, are just some of the things I would look at.