Ford F150 - Oil pressure problem.......

1991 f-150
When driving the truck a short distance it does fine, but after 30 miles or so and I come to a stop it will idle down along with the oil pressure and die. If I press the throttle and hold the rpm at about 1100 it will hold pressure, also after 10 min. or so of holding the pressure with my foot on throttle, it will hold pressure on it's owne. Where do I start looking for the problem????

First, get a cheapo aftermarket mechanical oil pressure gauge, hook it up temporarily (just leave it under the hood, or tuck it under a wiper), and find out what the pressure actually is.

Does this sound like I even have a oil pressure problem or does the engine idle too low..

Sounds like you need a real gauge. The factory one is fake.

The oil pressure gage is actually either on or off. It doesn't show exact pressure, just if it is above a specific set point.
Are the lifters ticking? If not then you probably don't have a pressure issue. Lifters are first on the food chain for oil delivery problems. I agree, get a real gage for troubleshooting.
Does it idle rough when it idles?

The lifters and truck sound good, that's why I can't understand where to look. It doesn't idle bad but it will idle down under 500 rpm when you make the long trip and then die out, I think that has something to do with my problem.

Does anyone have a idea of why the engine would idle down below 500 rpm and die out after driving 30 miles or so????????

Low fuel pressure. Low oil pressure.

Hey Steve is it only one place to install a oil gage?

In my 90 I had, the oil light would come on at a stop, it ended up being the motor, key word there "was" the 90 I had.

Yeah thats what Im afraid of but the truck only has 125,000 miles on it and my chevy has 237,000. Another thing is I have only had chevy's and I don't know anything about fords. The truck was my grandpaw's and he parked it in the barn when the problem started, and he was original owner and he took care of the truck.

That may be so, but you can never know when a oil pump goes out and poo cans your motor, it happens to any and all brands. If it was my grandpaws, I'd get it fixed no matter what.