Speedometer reads very high

So we exchanged the transmission with a rebuilt, and customer states speedometer was reading normal. Now it's reading extremely high. ABS light is on. Disconnected what Alex believes is VSS on top rear differential and speedometer still reads same. So at around 20-25 mph speedometer reads 90. Where does the instrument cluster get its speedometer signal from, right front wheel speed sensor, left front, or rear differential. Already tried a couple of differential oss on the transmission, although he doesn't think the speedometer gets a signal from there because it would differ as transmission shifts. As always I appreciate your time and knowledge, V