I have a similar issue with my 97 k1500 vortec 5.7. Runs great and never misses a beat until it’s over 90 out and when you go to restart after the engine is at normal operating temp it will start, run for a second then die. Only way to keep it running is to immediately give it gas and keep rpm about 1500 or more then it will run fine until you shut it off for a few mins and go to restart.
After replacing the coil, ignition module and checking all the grounds and connections still the same issue only when it’s very hot outside.
I think I may have finally solved it! The Vortec trucks and possibly the TBI trucks as well, Have two coolant temperature sensors the one on the side of the block that is a single wire connection at the sensor is only for the temperature gauge. The two pin sensor that screws into the water neck on the intake is for the computer and this is what a scan tool will read.
When the truck wouldn’t start, and it was hot out, I had my scan tool and no codes at all even when it fired up and died. The temperature on the scan tool was reading correctly, but then I saw -40 flash for a few seconds and then it went back to reading over 200. I’m going to replace the temperature sensor that goes into the water neck. Hopefully that finally solves my hot start problem and yours as well!