backinblackgtp 
ive been having the same problem for about a month now, so heres the situation i am in :
got tuned down to a 3.5 inch pulley with plenty of mods to support the drop, got it tuned, 13* timing, 10lbs boost.
while getting it tuned, i knew i had EGR problems, and i have a high flow cat, so i got the p0420 code deleted, since than my MPG has decreased from about 17.0 to 14.2 around town, i have NOT been pushing my car by any means, i let my car warm up for a few minutes since its cold here in NY, and than drive, i have replaced plugs,wires,BOTH 02 sensors, high flow cat has less than 10k miles on it and had a tune up about 10k miles ago as well. tried injector cleaner as well.
More importantly, when my car is cold, id say the first 10 minutes of driving, if i try and boost, my car misfires and the light blinks, i actually hear it struggling, the RPMS jump around, but than after about 10 minutes my car will be fine, no misfires, when i had it scaned it was cyl 6 that kept misfiring, so what could this be, is this just one big problem?
