This is not likely to be a problem with the rear axle VSS/ABS sensor.
Here's a quick check that you can try. With everything plugged in normally, throttle closed, engine off, ignition on:
Measure the TPS voltage between the gray/white and gray/red wires. The voltage should ideally be about 1.0V at closed throttle. If it is significantly greater, let's say roughly 1.5V or higher, the RPM may hang until the vehicle speed drops down near zero.