Why does this happen after driving for a 1/2 hr or so. Sometimes it feels like the car will hardly make it up the hill. There are a lot of spurts of power loss and if it feels continuous, I take my foot off the gas and it recovers to full power for a while. Also I noticed once it starts happening while I'm driving, if the tach needle gets above 2, that's when the power drops occur and sometimes it feels like the car is down shifting.