Battlefield 2 framerate issue

Just upgraded my system to the following, running windows XP home SP 2. I do not overclock my cpu or video card.

Biostar TF560 AM2 Motherboard Nforce 560
AMD Athlon 6000+ 3.0ghz Dual Core
2x1024mb(2 gig) G.Skill DD2800
Sapphire HD 2900pro 512mb 256-bit running at 600 core, 700 memory
Rosewill 600w Power Supply

I run the game with the following settings, though it doesn't seem to matter what settings I have.

Terrain: high
Effects: medium
Texture: high
Geometry: high
Lighting: medium
Dynamic Shadows: low
Dynamic light: medium
Anti-aliasing: 2x
Texture Filtering: high
view distance 100%

The problem I am having is this. When I first load the game, I will get framerate's between 85-100 no matter where I'm at or what I'm doing, be it flying, fighting, driving, etc etc. It's great, the game runs smooth and awesome. After about a half hour to an hour, my framerate will have dropped to about 55-70 and will eventually get so bad that every movement in the game is kind of jerky. Since this was a new system, i've been monitoring my system temps pretty regularly. The hottest my cpu will get is 46 Celsius in one of the cores, averaging out at about 42 c while running the game. Cpu idles between 28-34. Hard drives between 30-35.Video card runs between 55-65, idles at 50-52. . If the game gets laggy and I quit for a while and come back(earlier tonight was away for 45 minutes), the game will still be jerky while temps will be at normal idle ranges. Only a reboot will fix the problem. I can then play for another half hour or so and then the cycle starts over again.

I'm at wits end. I don't know where to even start with diagnosing this problem. All the equipment in my rig is about a month old or less, except for my soundcard, an Audigy 2 ZS. All settings in Catalyst Control Center set to let application decide. Only have about 30 processes running when I run the game.

Anybody have any idea's? I can provide more info if necessary.

P.S. The jerkyness in-game keep increasing till the game runs worse than it did on my old system. That was:
Asus a8n5x Socket 939
AMD Athlon 4000+ 2.4ghz single core(I overheated this chip at one point to over 96c and it still worked, though there was some definite loss in performance.)
4x512mb Corsair Value RAM PC3200. This memory only ran at 333mhz instead of 400mhz. Something to do with having 4 sticks of memory.
Sapphire x1650pro 256mb 128-bit running at lowest speeds available in Catalyst Control center(roughly 500 core, 600 memory if I remember correctly).

 

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