@Flashlab:
What Amiga are you using the card in? If you have the possibility, you should try it in a different Amiga and preferrably an Amiga with genuine Zorro-slots - like an A2000, A3000 or A4000.
A friend of mine had similar issues with his CV64 (distorted text) because of Zorro-bus issues. The previous owner of his A4000 had fitted it with a Buster 7 chip (a that old Buster is not supposed to be in an A4000, only A3000). This problem vanished when he got a proper Buster chip. So the Zorro-bus evidently worked, but not flawless and that made his CV64 output corrupted text for some reason. So I was thinking that it could perhaps be a Zorro-bus issue for you too.
Btw, regarding setting the horizontal frequency for a mode to 31.5KHz in Picasso96Mode doesnt automatically render you a usable mode. For example - if you would try to run a 800x600 screenmode in a horizontal frequency of 31.5KHz, that would result in a vertical frequency of probably below 50Hz which your monitor most likely cant display. It also depends on the timings - blanking-interval size for example.
/Patrik
