Fullscreen multimonitor resolution problem

I am using FS9 with 3 monitors on 2 7900GS 512 MB PCIE cards. In windowed mode all is fine. But when I use Fullscreen mode then the resolution on the first card is what I want, 1280*1024 32 bit, but on the second card (which is connected to the third monitor) the resolutions stays on 800*600, no matter what I set in the hardware Tab of FS9 under card 0 and card 1. FYI: the 3rd monitor is perfectly capable of runing 1280*102 32 bit, and even better, so that is not the problem.