Engine will stall when driving?

He checked and fixed also. Now, after all that, it will turn on and then die.

I recently acquired a 2001 Chevy Impala 3.8L. During the heat of the summer months my car will randomly stall while driving, usually during braking. The car will usually restart but will continue to stall out until it rests for about 15 minutes. The thing about this car is that it doesn't do it during any other season, just the summer. Also, when it recently had an episode of continuously stalling, I drove it up to our preferred mechanic. When trying to figure out what was wrong with the car, the mechanic couldn't get a code. Does anyone have any ideas where to start?

As far as I know there were no vacuum leaks. And it happens when the AC is both on and off. Sometimes blowing hot air through the vents can prolong the stalling, but it does not always work.

Thank you! What would be your second suspect? I'm looking to fix the problem once and for all.

Thank you so much!