Alright, so here it is. The motor is stock, but does have a 2.5in custom catback system and wants to run 91 octane, I'm averaging around 24mpg, and the thing misses when not under load ( idle, when i let off ect.) It is not a regular miss, so i don't suspect a mechanical issue such as valves. I checked for codes and the knock sensor is the only code showing. I don't think this could cause such an effect. The second thing is the plug color. Has any one seen plugs with RED (like iron color) insulator and side electrode? this is the appearance of 2 of the plugs, the other 2 are a purple color (it appears that they were red but are now slightly carboned) Clyinders 1 and 3 have purple plugs, 2 and 4 are red. Does know what's happening here?

thanks for your time