hazardous

Well I have an Evga 6800 and I'm having some problems. I softmodded the card with the latest version of Rivatuner and the latest official Nvidia drivers and everything runs flawlessly with no artifacts.

Okay so here is my problem. I go to run CS Source and I was running everything on "High" at 1152 by 864. I keep getting insane lag. At first I thought it was my connection and I checked only to see a ping of about 37. After several tests, my internet is not the problem. Then I realized that the card wasnt rendering fast enough, I was getting the lag but my teammates were not. I used the "net graph" whatever it is called command in the console and pulled up my FPS. I noticed that when I get the lag, my FPS is hitting about 10. So the problem is in fact my videocard. I can run 1152x864 at anywhere from 50 FPS to 100FPS no prob, so why is it suddenly dropping to 10????? It would be absolutley perfect for a minute or two, and then get so bad that I could not move. I thought maybe It was the fact that I was using a high screen resolution, so I dropped it to 1024 and still had the same problems despite having better frames per second when working normally. I would go from 100 down to 10FPS, and then 2 seconds later back up to 100FPS.

Why would a card run 100FPS consistantly and then suddenly keep dropping down to 10 and then back up? I dont think heat is the problem because the card has not been overclocked and I have several fans around it. Could it be inconsistant voltage? On a side note, I run WoW at 1152x864 with everthing maxed and my refresh rates are set at 75 hertz flawlessly. Any suggestions? This is killing me in important matches.