As far as I've learned, the higher the altitude the lower the MPG, and the less power you get as compared to sea level. This is mainly because the thinner air lowers the compression, if I understand correctly.

 

Yes but you are not high enough to have a great loss of power (air). Electronically controlled systems will lessen the fuel flow to keep the emissions down. At sea level more fuel must be injected to reach the ratio of approximately 14.8:1. It reduces your fuel economy for emissions. Now much more than 6500 ft above sea level your economy, power, and emission will start to drop because the engine now must try to maintain running itself properly especially 9000+ vehicles really start to struggle run properly.

 

good info, now I just have to get the beater I bought home and get it running. makes a crap load of noise from the timing cover, timing chains here I come.

 

I average about 16-17 MPG now that I no longer run the oversized tires. I have gotten as high as 19 taking it easy on the highway but can't seem to go over 20 no matter what. Having said that, my D has the original plugs in it so I may be able to make it happen if get off my **** and change the plugs and clean the IAC.