Really hate ressurecting a really long dead thread, but I'm having the exact same issue, except I'm using the proper clock chip.
I can either have my speed horribly fast at vss count of 8305, or have it be accurate at somewhere around 13000. It's an 04 Honda Civic. I know I have the wires right, and I know that the car is reading accurate speeds (I know when I'm doing 90mph, and when I'm doing 65
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).
So, any ideas on where I should be looking?