Other Fuel System Tank Mounting problems of the 2009 Toyota Corolla

After filling the gas tank and driving up a hill the check engine light (cel) came on and the engine ran rough. I nursed the car up the hill and drove home. I found the gas cap was not tight even though it had been clicked one time when the tank was filled just a few minutes earlier. A search for this on the internet revealed that others have had this same problem. I tightened it to one click, of course. A few days later I bought a Toyota gas cap at a local Toyota dealership. This sequence repeated multiple times; cel turned on, engine runs rough, lose of engine power. In one instance I was passing a car on a four lane highway when the engine hesitated and the cel turned on. In another instance I was turning left to go slowly up a steep hill when it happened again. In every instance the gas cap was loose. It happened once when I started the engine in a parking lot. I've come to the point of checking the gas cap to be sure it was tight every time before I start the engine. In early 2015 I bought another new Toyota gas cap at a Toyota dealer. It's now March 31. This same sequence of events. . . Cel comes on, engine runs rough, lose of power for about 15 seconds. . . Has happened about 12 times with this newest gas cap in less than three months. I always tighten the gas cap to the first click as it should be. This can be dangerous if it happens when we need maximum engine power, as in passing. A search on the internet shows that others have had this same problem. Comments on buying new Toyota gas caps at amazon show that still others are struggling with this. I can understand fair wear and tear on the "o" ring in the cap. But when two new caps come loose after being clicked as instructed then something is not right. Mechanics at the dealership don't have a good answer for this.