How do you manually add the resolutions?
The whole program works with drag and drop. Once you understood this, it is very easy to use.
Take the box icon (the left most) with the mouse and drop it into the resolutions list on the bottom left. This gives you a new entry and the width and height fields become active so that you can overtype them. Enter the resolution you want to create. Press Enter or Tab in each field so that they are shown in the list.
Once that's done, take the box icon again and drag it into the color format list on the top right. This gives you an entry with 256 colors. Below the list you can adjust frequencies to match your monitor's specs. When you think frequencies are fine, click on use and on test.
When the test is successful, take the entry from the list and drag it onto the copy icon (the second from the right, next to the skull). This will duplicate the mode. Select the copy, change color from 256 to high color and click on use. Now drag the high color entry to the copy icon, change the second copy to true color and click on use again.
Now you've got a new resolution. Repeat all the steps for yet another resolution until you got all desired resolutions in all color modes.
If you don't like an entry, take it with the mouse and drop it over the skull icon in order to delete it.