2002 Mazda Tribute trouble with warm starts

I recently was driving my car and stopped at the store. I came out 10 minutes later and could not get my car started. It did crank. I would have bet my paycheck that it was not the battery. I left the car on the parking lot over night. The next morning it started just fine. I took it to the shop. I was told that my problem was the battery. I now have a new battery. Eight weeks later the very same thing happened. The shop is unable to duplicate the problem. It only happens on warm starts. The shop suggested getting a new fuel pump at the cost of $900.00. I wouldn't hesitate if I really felt this would take care of the problem. Any suggestions?