Why wont my van stay running?

i have a 98 plymouth voyager. i tried to jump off a friend's car and while doing so, mine died. we were able to get someone else to jump me off, but it did not stay running. the next day i put in a brand new battery and it started and i was able to drive it the 50 miles to my house. from there i went to autozone and tested the alternator and they said it and the battery were fine. but now i cannot start my van without being jumped off and then it does not stay running for more than a few minutes. what do you think is wrong with my van??? please help!!!!