Originally Posted by 95geo
because when you add a chip it changes the injection pulse width and timing from what the ecm/pcm "knows" and it no longer knows how much fuel is being put into the cylinder.
i have been towing with 500hp recently and i have been getting 14.5-15mpg on 35" tires. i have gotten a best of 17 towing and 19 unloaded. i have yet to run my mileage tune which should net me about 21-22 mpg if driven conservatively.
this is with an 04.5 duramax/allison and tuned with efi live. i wouldnt run more than a 60-70hp chip unless you plan on trans upgrades. exhaust should be done reguardless becasue it drops your egt's about 100* and helps the turbo spool quicker.
Are you running the "moonshine" tune? if not, who's tune are you running or did you make it?
That efilive is pretty sweet but I'm not going to buy it until I build up my trans.