I am having a problem with a 2000 Dodge Ram I just replaced the blower in the truck and is working fine but the airflow comes and goes like some kind of door in the air box is moving back and forth or something like that. There doesn't seem to be any pattern the airflow will be fine and then it will go away while blower is still audible and is blowing fine. any help will be appreciated.

 

Sounds to me like you have a vacuum leak. Search the forums for 'wild vents'. In the threads, it will talk about a check valve that is usually the problem and needs to be replaced. Very easy start, too. Only about a three dollar, one minute fix.