GMC Repair: battery keeps going dead, astro van, altenator

Question
Pete I have already tested my altenator and got a new battery also tested the starter and the battery still keeps going dead.  I have a 90 Astro van six cylinder 4.3  when you go to start it turns the motor over but it wont start eventually the battery runs down from trying.  Is there anything else that can run the battery down besides the altenator?  I'm at my wits end with this van because it was running fine after we bought the new battery for a whole two weeks and just last night i went out and it was completely dead again.  Help please. Thanks  

Answer
Hello hun
this sounds does sound like a bad reg in the alt .
try this get back to me after you try it start the van up pull the battery cables while the van is runing if the van stalls then the alt is bad . and that would be the reg in side the alt.

iwill help u all i can we will find the trouble pete