1998 Chevy Blazer shutting down on long drives

I was driving for about two hours, about 90 miles from home when I noticed suddenly that I could not accelerate. (It was the middle of the day and hot outside.) When I hit the gas the car sputtered (like it was missing almost) and came to a hault.

After letting the car set for a half hour it would start up, after which I'd get about 5 miles and it would happen again. I finally limped it to a parts shop where I got a reading saying that O2 sensors bank one sensors 1 and 2 were reading low voltage.( I have four O2 sensors) I replaced them and drove about 50 miles home without trouble. (When I drove home it was dark and cool outside.) I also drove about 40 miles that evening without any signs of trouble.

I continued through the week, any hour of the day, without trouble. My average drive was only about 10 miles.

A week later, this time 100 miles away and in the dead of a summer day, it happened again. This time I allowed the car to set about a half hour, it made it about 5 miles and shut down again. I got another reading, and it showed the same error on the same O2 sensors. ( I only unplugged the battery for about 5 minutes, perhaps the computer didn't reset?) I let the car set for several hours until it started to cool down outside and I drove about 80 miles home without any trouble again.

I've replaced two of 4 O2 sensors (which read low voltage) and aside from that I have no clue. I've checked the Catalytic converter after short trips and it didn't seem to be glowing. What should I look for next? It seems to only happen when it's hot outside and I have driven for over 80 miles.

I recently replaced the radiator, about a week before the first incident.

Any ideas? I would greatly appreciate your help!

Jeff