Can you post a picture? How old was the tree when you planted it? Was it a bare root tree or had it been container grown? Were there leaves out when you planted it?
All those questions will help, but I'm leaning towards transplant shock, even though 6 to 8 weeks seems a long time. It might have been doing OK and then it got really hot and it just doesn't have the 'small root' qty it needs to draw in the moisture. Is it in the full sun?
