2000 blazer stalling

I have had a problem with my blazer stalling after driving it about 70 miles on the freeway after I exit it will shift hard out of first gear then after a few miles will stall. After pulling over and waiting for a couple of minutes it will start and drive ok. I have noticed the 2 times this has happened it was hot outside and I had the a/c running and I had no problems on my way back with the a/c off.. Any ideas and help with this problem will be much appreciated..

Check for lose of fuel pressure and or spark when it stalls.