I would also check for guardian problems. If your water pressure drops for more than a few seconds you will get the guardian set which will put you back to %90 power. If it continues to have lower water pressure it will go to even less power. You should see/hear the alarm though when this happens. You can clear it usually by cycling the key a few times.

I have had this problem a few times and ended up getting some harnesses from whipple which prevent the code by showing a higher amount of pressure using a resistor.

As stated above, check your tune. If you have Silent choice check the linkage and make sure its intact. I had a similar problem once, and all it was, is that one of the linkages broke.

What are the gap specs for the 41-983? BTW, Great prices on those plugs from summit racing.....

pretty sure the gap was .060 but specs should be on your flame arrestor cover