This sound like a textbook example of a blower motor resistor failure. The resistor is what controls the speed of the motor, simply put the switch sends power though different curciuts in the resistor which changes the speed. The lower three settings slow the electicity, which slows the motor. The top setting is a battery voltage "pass through", the high speed will eventually fail is the resistor is not replaced.
The resistor is located behind the glove box and fairly easy to replace.
1) Disconnect and isolate the neg battery cable.
2) Open glove box door to access resistor.
3) Pull out lock on blower motor resitor harness
connector to unlock the connector latch.
4) Press down on the latch on the blower motor resistor harness connector and dissconnect the wire harness from the resistor
5) Remove the two screws that secure the blower motor resistor to the HVAC housing and remove the resistor.
Reverse to install, torque screws to 17 in-lb (2 Nm)
This is the R&R from my database.
The resistor may be available from you local parts store but check the price at your local Jeep dealer as well, sometimes with electrical parts they are less expensive at the dealer and even if you buy them and install them yourself Chrysler parts come with a 12 month warranty.
Let me know if this helps.
Wednesday, September 30th, 2009 AT 10:13 AM