You might try using the "gtf" program to generate a modeline.
This example is for your stated resolution, at a 60 hz refresh rate.
Make sure that your monitor can handle this resolution. Also, you won't get more colors using 32 bit over 24 bit. The extra bits are for overlay information, which you may not be using.
The gtf program, "
General
Timing
Formula", is a part of your xorg installation, so you should have it already.