Misbehavior of a 8 year old Mystique

I drive a 2000 mercury mystique and I have already replaced a fuel pump. In addition, the check engine light is on with a Cam Sensor code.

Here is the problem: 1 year ago we were driving to Kansas in the extreme heat and humidity. Every time we would go up a hill, the car would shut down. We could pull over, and restart without a problem and drive as if nothing would happen. Several miles later, it would happen again. We drove the car all winter long without problems. Now that summer has returned, the car shuts down after several hours of driving.

We changed the fuel filter, a coolant valve, and that did not fix the problem. Another seemingly related issue is that sometimes when I fill the car with gas the pump at the gas station thinks the car is full. Also, the car doesn’t usually release air when the gas cap is removed. Is it possible that air is going into the fuel pump? Why would the car go all winter long without issue and beging having problems again in the summer?

Another small issue is that after the fuel pump went out in 2002, the gas light has gone on at 1/4 tank whereas it used to.