The rear axle has the VSS/ABS sensor. It does double duty. You will find it on the top of the rear differential. Remove it, clean it, replace it. If your still getting the code, buy a new one.
VSS/OSS on the transmissions are found in 2wd only vehicles, and that is for 95-97 only I believe. You have a tone ring in the axle that the sensor reads, and the ECM reads that signal then converts it for your speedometer/odometer.