UT3 - Random stuttering?

Just built my new system

Core 2 Duo 3.14 (E8500)
ASUS P5Q Pro LGA 775 Intel P45 ATX Intel Motherboard
4 GB OCZ DDR2 RAM
500 GB HD
SAPPHIRE 100242L Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16
Vista 64

My old system wouldnt even run the UT3 demo... so I finally got around to building a new one. Loaded the deom. Beautiful! 1680x1050 res.. smooth as silk.

Now I bought the full game, loaded it up....(patched to 1.3) and well.. every so often I get an odd, stutter. like laggin, but pings are good (70-80)
I tried choose different resolutions, but doesnt make a difference

are there any tweaks I should know about? (Like in COD4 you HAVE to turn off Antivirus or you get freezing during bombings)

any help would be greatly appreciated. the game is awesome so far (only got to play a few maps last night). its like old school UT99 but with awesome graphics!

THANKS!!!