There are several things you can do using the boot: cheat codes but remember that nothing is permenant unless your saving your configuration when you logout...
You can specify resolution, X, and Y, frequencies on boot. Example from the cheat code list:
boot: knoppix screen=1280x1024 xvrefresh=60 xhrefresh=80
I also had a problem with 3.7 resolution and found that once in KDE you can open a terminal and type:
This will allow you to specify the monitor from a manufatures list or manually enter the specs.
Don't know if all these will work for 3.8.1 though, but most I believe are unchanged.