ViewSonic monitor problem

My old CRT monitor burned out and I've replaced it with a ViewSonic VG2030WM, which has a resolution of 1680 X 1050 @ 60Hz. Kudzu (or whatever configures new hardware) set it to 1280 X 1024 & 60Hz, which works fine, although everything is a little larger than I want. The monitor model isn't listed in system-config-display so I've set this to the generic "LCD Panel 1680 X 1050". But when under "Display Settings" I set the resolution to 1680 X 1050, the next time I try logging in or rebooting the monitor hangs the system. Exactly how I get around this isn't clear -- sometimes the system goes back to 1280 X 1024 after several attempts to reboot, and once I got the screen back by starting to type something at the command line login prompt that appears briefly before X starts. The problem is not with the monitor, as it works fine with the recommended resolution of 1680 X 1050 when I bring up the dual booting Windows XP system. Any suggestions at how to proceed to get a higher resolution on this monitor with FC6 and a gnome desktop? Thanks for the help. Jerry