I have a 1990 300 te.. it has been a work in progress, but i have a big one on my hands...I am in Georgia and we have been in a extended heat way. What i notice recently every time i drive on the on the highway and i am driving at 65 mph or more (shhhh dont tell) for more than 10 minutes where the rmp is more than 2500.The oil gauge needle falls to 1 or 0. At that point i begin to hear the valves. If i slow down to about 50~55 for the same amount of time (5~10 mins) the valves sounds cease and the needle goes back up to 3..

I have checked the oil and it is at the recommended level. I am using 15~50 synthetic Mobil 1 oil.Lastly the car is not over heating and it runs perfect.

My question is what could the problem be?? I read something which stated it might be the oil pump.
waiting for anyone input