1993 Pontiac Bonneville Car runs bad in high temps

I have a 93 Bonneville 3.8 that seems to run ok when the weather was cold. As the weather gets hotter, or if I'm in rush hour traffic for an extended time on a cooler day, the car seems to run as if it is out of gas. On a hot day, like yesterday when it was in the upper 90's, the only way I can drive the car is by barely touching the gas pedal. If I press the pedal very hard the car falls on it's face and will eventually gets to where I cannot go over 20 miles per hour and the car has no power to pull up a hill. It will also sometimes quit if I come to a stop. I can turn the car off and wait 5 minutes and the car will start back and be somewhat driveable for another mile or two.

I have changed a dozen or so fuel filters, checked the fuel pressure (40 pounds no running and 36 when idle, and goes to 40 when pressing the gas), changed the mass airflow sensor, cleaned the throttle body intake, changed the thermostat, and the air temperature sensor. I also had the exhaust checked to see if the cat was stopped up and it was fine.

Any help with this problem will be thoroughly appreciated!