keyless entry prob

My mom has a 99 GMC suburban. Here recently it has had this problem with the keyless entry. Sometimes the door clicker dosen't work at all. When it does work sometimes only one or two doors will unlock. Come to think of it only some of the doors will lock or unlock when you push the button in the truck. I'm thinkin its got somethin to do with the power door lock control module and reciver. Any advice?