heater motor speeds

My 2000 Venture heater motor is not working right. It is a 5 speed motor. Last year I lost motor speed 1 and 2 recently i lost 3 and 4. I now only have speed 3 high. Any ideas. I doesnt make sense that the motor is bad.
Thanks John

It could be your blower motor resistor giving you the problem. Here is a link to a diagram of it's location:http://autorepair.about.com/library/a/1h/bl251h.htm

Thanks you are correct. I went to the dealer and bought a new blower motor resistor for $31 and it worked fine. It was a pain to put in. It is located on the passenger side behind the glove box. If you look under the dash you will see the blower motor and behind that the resistor. There are 3 screws holding it in. one is harder then the next to get out but do able for a semi handy person. I called Pep boys and they said the labor would be about $60 so i figured it had to be a not that difficult.