I bet it's not the pump, it's the plumbing. It don't have a large enough inlet line to feed the pump during hot weather. The inlet should always be bigger than the discharge on any pump. Even if your inlet is bigger than the discharge now, it's either not big enough still or the pump is mounted wrong.

Gas is one of the most difficult things to pump and most people don't understand that and blame the pump.

Make sure if possible that the pump is gravity feed with a large inlet line and it won't do that. Is that always possible? No not always without a custom tank.