In cold (less than 45F) weather, the power lift gate on my 2011 MKX raises normally but when it gets to the top, the jounce at the end causes enough rebound to start the self closing cycle. Closing can be stopped by hand, but it's a bit annoying. I just checked today when it's around 50F and there is a rebound but not enough to start the cycle. So, replace the air cylinders and see what happens?