Pictures become slow and delayed

Hello

I'm using Color 1.5 and FC7, if I'm grading or editing everything starts working fine, but after 5 to 10 mins or so my second display(monitor out) begins to slow down and the images feeding it become delayed and very slow to update(compared to the application's display), to the point I have to save what I'm doing and restart the application, then it all starts up fine with quick video updates, but then it slows down again, and the cycle repeats itself.

is anyone else having this problem?

is this a Snow Leopard problem?

is this related to latest pro apps update?

mainly when grading HD, did a SD project no delay.

after a while it becomes anoying, having to stop and restart FC7 when editing or Color when grading.

a solution for FC is the option f12 a/v device refresh, but how to do that in Color?

my setup

MacPro early 2008
snow leopard 10.6.1
Nvidia GTX 285
Matrox MXO with 2.1.5 latest driver
18 gigs or RAM
5 drive internal raid 0 500mb/sec read/write
1 drive for booting and apps.
FC7.0.1
Color 1.5.1

I also know someone else with the same problem running FCP 7.01 and Leopard 10.5.8. with a ATI Radeon HD 4850, and also Matrox MXO.

thanks in advance