what could it be
 

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

Definately sounds oil pump related, such that I would not continue to drive it until the oil pan is pulled and the oil pump is inspected. My guess is that there is considerable debris blocking the oil pump pickup tube.

Oil pump OR oil pump pick-up issue is most likely.

Have you tried lowering the oil level to below the LOW mark & see if it still happens.

I have not tried lowering the oil... i will try that.. Because i about ready to change the oil