wwiiavfan

I re-read this thread but I didn’t see anyone mention if the gas tank vent/charcoal canister has been checked. If that system is blocked/ defective, you could be starving the pump due to no air getting into the tank. Easy to check, when it starts to die, quickly pop the gas cap off to make sure air is getting into the tank. If it recovers, your vent system is defective.
You could also try to determine if the issue is heat-related or if it just takes a certain amount of time to present itself (like the above mentioned vent issue). Try idling for a long time with hood open and some big fans blowing air thru the rad and on the engine. Maybe even some ice on the intake/ fuel line. If doing this prevents it from dying, you know it’s heat related.

Danish Shark

Check if you have vacuum building up in the tank

Edit, I see wwiiavfan beat me to it