Had the same problem with my 99 about 3-4 years ago. I thought it had to be a wiper control problem. Used my voltmeter & tested the motor control signals at the wiper motor connector, & control signals looked OK. I replaced the motor, everything's been OK since (with the front wipers that is).
From what I remember, for intermittent wipers, the motor gets a pulse to start a cycle, then the motor parks at the end of the cycle. For continuous wipers, the motor gets a continuous voltage. The wipers then park when the voltage (signal) is goes low.
Good luck.