After updating to XFree86 3.3.3.1 via the RPMs on updates.redhat.com, my monitor/video card are no longer getting the correct hsync and vsync. I have a Diamond Viper 330 card, and a MAG DJ530 monitor, and was attempting to set up 800x600x32bpp mode. I've rerun xf86config several times, and tried commenting out modelines to make sure it selects the right ones. All this was working great before the update.
We currently do not have a Diamond Viper 330 video card to replicate this problem with. We will need to get one into our test lab as soon as possible. Until then you may want to try our supported mailing lists at http://archive.redhat.com to see if anyone else has posted a solution to this issue.
I backdated to the 3.3.2.3 version that comes with the 5.2 dist, and the problem disappeared. I am looking for the 3.3.3 update RPM's that were posted before the 3.3.3.1 release, because that version also worked fine.
Have not verified yet but I may have found the reason for this. The main XFree86-3.3.3.1 package contains /usr/X11R6/lib//X11/XF86Config. This is a change of location from /etc/X11/XF86Config, and this path is looked at BEFORE /etc/X11. Hence, changes to /etc/X11/XF86Config were not taking effect.
Actually, disregard previous comment as I see it's actually a link to /etc/X11. Sorry about that... I saw the path problem on another system and thought it might apply here.