I've had this problem for a few months but I haven't posted anything on it.
When I start playing the game, I get low frame rates. In order to correct the issue I switch from either VSync on or VSync off. Once switched from on to off I get 80+ FPS vs( 20+ with Vysnc on.)
Similarly switching from Vysnc off from the start to Vysnc on locks my frames at 60 FPS vs (20+ with Vysnc off.)
SPEC
i7 920 @ 3.6GHZ
12 GB DD3
HD 5970 Dual GPU card
Installed on a 64 GB SSD
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