2001 Ford F-150 01 Ford F-150 Oil Light

I have an '01 F150 w/ about 155k miles. Anytime the truck sits long enough to cool down, the oil light will come on and show no pressure upon startup. If I let the truck sit and idle, it usually goes off in about 5 minutes (same if I go ahead and drive).

Generally it will bounce from mid range pressure to zero pressure a couple of times before it goes off for good.

Generally this problem is lessened (but does not go away) right after an oil change.

Generally it drives perfect, even with the light on. When it's really cold (below freezing) the engine will actually bogg down and not accelerate strong. However, this will only last for a minute max. Once the truck gets warm it runs perfect. As good as the day I bought it.

The truck really runs perfect but I need to be sure I'm not destroying the motor. Any thoughts you have will be greatly appreciated.

Also, probably not related, but I will let you judge. When my undercarrage gets really wet (i.E. Rain or carwash) I will get a missfire (and it's a loud, banging misfire that I can feel with my foot on the accellerator). Plugs & wires are all well connected and fairly new (30k miles).

In the rain, it is constant and can't get much above 40mph. After a carwash, it is less severe and goes away after a 10-15 mintues and the truck dries off.

Thanks for all you guys do.