Oil pressure gets really low after driving my Jeep at high speeds for a while. While on the highway it's right in the center of the gauge (40). When I get off the highway, it gets pretty low but not low enough to trigger 'Check Gauges' warning. However, if I shut it off after highway driving (ex: get gas) and then start it up, the pressure is extremely low and 'Check Gauges' comes on. It looks like it's going to go up for a few seconds but then falls back down. So I shut it off, wait about five minutes, fire it back up and it slowly creeps into normal range. Usually takes about 30 secs to get into normal range on the second go around. On about 2 or 3 occasions while driving around town, the pressure got up towards the upper spectrum of the gauge when stopped at a light but would then go back to the normal range when I started driving again. I change the oil about every 3k miles and the oil level has never been low. Any idea what might be causing this? I would guess the gauge is faulty, but wanted some other opinions. I never hear any odd sounds or anything like that. Thanks in advance.