need help finding vss --speed sensor

i can't seem to locate the speed sensor i even have a haynes auto book but no help...my speedometer jumps every now and then but any other time it does not work ...they told me it might be the small gear inside the speed senor ...the gear is cheap but does no good cuz i can't find the speed sensor .lol.... my probe (wich is automatic:( ) won't shift into to od so i have no final gear and i rev 4.5-5.5 at 50 mph (guessing)
so if you can help me please do.