i just bought my 04 GT and it came with a diablosport pred tuner. the guy i got it from showed me how to use it kinda. instead of messing with it too much i just installed the tune that came with it. thing is i went from 18 mpg down to 11. what could be the reason for that? could it be because there is other mods on the car or what? i have never used a tuner before but from the research that i did there is supposed to be an option for 87 91 or 93 tune and i dont have any of those options. any help would be awesome. or a step by step instruction on how to download the tune i need possible?