1999 Chevy Astro Engine dies after starting warm or cold

Electrical problem
1999 Chevy Astro 6 cyl Two Wheel Drive Automatic 255K miles

6 months ago the van would not start after driving it for 20 minutes. I took the fuel pump relay out let it cool down & then put it back b/c it seemed like I didn't hear the pump noise. It started up and drove ok. 2 months later while driving in 110 heat in las vegas the van stopped in traffic & would not start. That same day it would sometimes die at stoplights in but always start right back up. Seemed like heat was getting to the relays. In vegas I cooled down the relay with an ice chest and left the top fuse cover off. It started right back up and ran fine. When I got home I replaced the fuel pump relay and everything was ok. Now 2 months later the problem is back. The van dies after I start it up for the first time or in the last 2 weeks it will die after it has been run for 30 minutes. [It dies immediately after restart] The fuel pump was replaced 2 years ago. Seems like the problem is the fuel pump relay but that has been replaced with one from autozone.