Battlefield 4 LOW FPS!

Hello everybody... i got a problem with BF4.
I am having some problems with FPS in Battlefield for, not the BETA but the Official game.
In TESTE RANGE, i tested my game specs and saw that it ran Battlefield 4 on Ultra at 50 to 60 FPS.
If i turned it to High then the FPS boosted up to 70 FPS, and at times to 80.
In Battlefield 3 i had 70 FPS on ULTRA on all servers.
However in Battlefield 4 multyplayer i get low fps close to 40, on almost all settings above MEDIUM... on low i get a good 90 FPS but with sudden drops to 40 and some times 30.
This looks more like a bug or something else, any clue how to fix this or who else has the same problem?
Or maybe my GPU is so outdated that it can't keep up?

My specs are.
GPU: Single AMD Sapphire Radean HD 6990 4gig DDR5.
CPU: AMD Phenom 6 core, 3ghz.
RAM: 8 Gig Kingston.
OS: Windows 7 Ultimate 64 bit.
All drivers updated and Resolution on A single monitor: 1920x1080.
 FPS in BF3 on ULTRA and everything MAX 75 FPS easy.

No clue what to do... get an Upgrade on the GPU or what.
If you guys have the same problem with your Setup please let me know, if you have an idea how to fix... please tell me.