Backfire/Misfire at high RPM's

[cobrakiller02]

I have an 02 WS6 A4. It has Longtube headers, Xpipe no cats and true dual SLP loudmouth exhaust. While just driving normally it runs fine but when I put my foot in it it will backfire from about 4500 to 6200 rpm's. The other day I put 93 octane and 104 octane booster in it and it straightened it out alot but not all of the way. Has anybody had the same problem or anything similar? Or does anybody possibly know why it is doing this? Your help is greatly appreciated! Do you think it might just need a tune?

[Fearls1]

I have lots of loud popping and backfiring going on. Pretty sure its my crappy FM muffler that is rusting out inside.

[ExStanger]

Open your hood at night with the engine running and the lights off and look for any arcing plug wires.

[cobrakiller02]

Alright, I really appreciate the advice man.