[s-cars] loss of power and high rpm backfire

[Elijahallen92 at aol.com]

Hi, in addition to my recent loss of power which I am thinking knock sensors, 
is a kind of light backfire at 6000+ rpms at full boost. It doesn't happen 
every time but if I'm driving the car hard it will do it more and more. It 
feels/sounds like two or three small backfires as well as slight loss of power at 
every backfire. I have had a similar issue before and it was plugs but I've 
changed the plugs and its still doing it. Now I wonder if this is something 
related to the loss of power I'm having when going to full throttle at or below 
3000 rpms and having the timing be cut way back. The car has 150K miles on it 
with original coils so thats also a concern of mine. Any ideas what could be 
causing these problems. Thanks for any help.

Elijah