On my 2003 Dodge Durango, what would cause the a.c. not to cool as much ?

Have you checked the refrigerant pressures are OK, check the cabin air filter is not restricted if applicable, and that the condenser fan is working.There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online

It could be the blower motor. I have same issues and I found this answer under a different question but sounds like same issue .