From my experience, resolution problems are best dealt with in the PCC (Configure your computer)
Press the PCC button (circle with a wrench) and, after entering your admin password, select Hardware
> Configure video card.
First, under Monitor, choose your particular type (mine is Flat Panel 1366X768)
Then, under Resolution, if the desired setting is not shown, choose Other and there you will find an exhaustive list. Make your selection and after pressing Quit, you will be advised to log out to make the settings stick. No need to completely reboot just log out and then back in and you should be good to go.