No accelerator response

The title is not the entire story. Car: 2008 Kia Sportage 4 cyl. 72100 miles. Yesterday my wife stopped for gas and had a difficult time removing the gas cap. "Feels like there is a vacuum in the tank". However she got gas and came on home (about 7 miles). This AM car started fine and she drove out the driveway (about 700 feet). When she got onto the highway, she was limited to 20 mph. She brought the car back and went to work in the Jeep. I started the Sportage, no check engine or other lights, idled about 1000 rpm and stayed there as the accelerator pedal was pressed to the floorboard. Since it was still dark I continued my coffee and waited for daylight. While sitting there I recalled the problem the night before. When it was light enough, I opened the gas cap, in so doing there was a loud click then it turned easily. Replaced the cap and started the car-all normal. Drove it several times today with no problem. Any relation between these two events or just coincidental?
Any suggestions would be appreciated as this is my wife's transportation to Jacksonville 5 days per week.