Check your gauge for accuracy first of all. Are the other gauges reading correctly too, as far as you know? Or could the fuel and temp gauges be reading a bit low too? If they're all a bit low, it could be either your IVR or a bad wire/connection not allowing enough current to get to the gauges.
If it is that low, that's a bit too low. Getting below 10 even at idle is not a good thing. The old idiot lights tended to come on between 4 and 6 psi, if I remember, so that's getting into the light-on territory.
Ford calls for 40 to 70 psi range, so you might have to check into a few things if it turns out you're getting near zero pressure at some point.
In that case, thicker oil at the very least.
The 40 psi is really not that bad. Even the 25 to 30 when warm and driving is lower than normal for a Bronco, but isn't so far as to really worry that much either.
It's that 10 and below that is not anywhere near normal.
Some things to think about are:
Old worn out pump. Very unusual, but not completely unheard of either.
Old worn out main, rod and especially cam bearings. Also a bit strange at only 82k, but again, not unheard of. Especially if a PO wasn't very good about changing oil regularly and/or abusive to the engine.
A galley plug leak that is not bad, but gets worse as temperature rises. I think most galley plugs will show a leak on the outside though, so not sure that's an option here. Can't remember if there are plugs in the front under the cover, but if so, one of those leaking would not show up on the outside. The rear would likely drip down and look like a rear main leak.
Not really trying to be all doom-and-gloom on you, but as low pressure goes, yours is a bit lower than advisable in the long-run.
First things first though. Check and compare your gauge to make sure you're getting a correct reading. My gut feeling though, is that even if the gauge is off, that drop at idle when it gets warm is telling you something. Mine would start up at 70 when cold and idle at 40 all day long no matter what temp. I used 20w/50 oil in mine, but that was back in the day and I prefer thinner oils now. However, maybe yours needs a little help and that thicker oil is called for again.
Good luck. Let us know what you find.
Paul