oil pressure problem 89-302

I have a 89 bronco with 302 with oil pressure problems. It's ok until the engine gets warm , but then it drop.There is no bad noise to hear from the engine.If you would press on the gas the pressure would go up, but would fall back of when you let up.It seems like it is either high pressure or nothing at all. nothing in between.
I have changed the oil pressure unit.But the problem is still there.
The engine has only 78 000 miles on it.

There has to be someone out there with same problem .
There are no to many of these cars i norway, so there are not so many people to ask over here.

You may not have a problem.Check the oil pressure with a mechanical gauge .Put the gauge in where the sending unit is.At normal engine temp-not sure of the exact specs-if you see 15psi at idle and app.40-50 psi at 2000 rpm your OK.

Do you change your oil on a regular basis? What do you use for a filter? Also next time you change your oil replace a quart of oil with Marvels Mystery Oil. Could be a dirty oil pickup screen, and MMO will clean all that garbage out of your engine. MMO is composed of hydrocarbons, which will break down that slduge. In no way is MMO snake oil, i do not want to hear it. It will thin your a little bit, not as much as you think. Thinning the oil is not how MMO works, it is the Hydrocarbons at work. Change the oil in about a 1000 miles because the stuff will really clean out your engine, and drain it when hot to get all of the garbage out. If you do not hear any noises, do what Bronco2 said first. Because usually with low oil pressure you will hear lifter rattle.