When the trans is whining and shifting hard it is a bit more harsh on parts but it isnt really hurting anything to where you need to be concerned that it will fall apart or cause excess damage. The idea is to prevent slippage and burning up the trans. Without scanning your car to view data it is hard to say exactly if that is your cause and that is why I always suggest taking the car into a trans expert for a good diag to determine the cause of the problem. Generally when a pressure control solenoid is going bad it will act up after the trans warms up or you have driven for a short while. Going down the highway for a long time is not going to make the problem happen because you are not cycling through shifts starting off in 1st gear while cruising along. It may take the car until you come to a stop after this long highway jaunt and making a few shift cycles before the problem exists and at that time it will see slippage during the shifts and throw the code and max out the line pressure and you will hear the noise and feel the harsh shifts.
