locovaca is correct... Ranger VSS's are found in the transmission tail shaft area, and where applicable ABS sensors (also called VSS's) are found on top of the rear pumpkin (I believe that 4x4's have an ABS sensor is each front wheel, too). If you can't find the location of your VSS's, your parts store should have a diagram on their computer of where they're located.
When my transmission was acting up I changed the ABS VSS sensor in the pumpkin and my transmission started shifting normally again. Whether the sensor change had anything to do with my trans acting normally again I don't know, but I do know that now it works and I'm happy.