Short of it is the resistor controls the fan speeds for the blower. Easy to replace and to my knowledge only available through a dealer.
The resistor is under the passenger dash just left of the blower motor
should be the connector in the ac housing closest to the blower motor
behind the glove box
This website might be helpful.www.dodgeparts.com/
No such part exists
The blower motor speed resistor is burned out.
Behind the glove box.
It is under the dash, behind the glove box.
Your truck has both. the resistor is between the switch & blower.thje resistor controls the blower speed
It's close to the blower motor.
You need to replace blower motor resistor.
When you beat the blower motor, you are probably shaking the blower resister. The resister is what controls the blower speeds and is probably bad or loose.