That's just not so at all. The oil pressure in my LT1 Vette (with over 100k miles) drops to 40 at idle with a hot engine.
And it may go to 30 or a tad under if it's a really really hot day with a hotter than normal engine.
If your gauge is telling you the truth, your oil pressure is low due to bearing wear. That can be considered "normal" with an engine that has a lot of miles.
But generally, dipping to almost the red zone is not normal. You might want to run with oil that has a higher viscosity than what you're using now.
If you see a noticeable jump in oil pressure, you know it's due to engine wear.

 

I would find it hard to believe a replacement engine with 80-90k would have that much wear. Plus it runs to good imo.

 

I've seen engines spin bearings and destroy it with 50k on them. A little neglect and some abuse can cause some damage.

 

I think if anything would be the problem it would be the pick up.. I'll go take a rubber mallet to the oil pan tomorrow when i get the change and see if anything bunches around.

Edit: Just to add. I don't hear any abnormal sounds from the engine. I drove it on the Interstate last night at 80 mph for roughly 45 miles with no problems at all.

 

I'll drive the thing to work tomorrow, and leave it running when i pull in to the parking spot. If the oil pressure go's up to middle I'll know for sure if its the pick up off the oil pump.

 

I think the operation is normal. Wahen you increase the rpm and the psi goes up thats normal. When you slow down and let off the gas, the psi drops. Thats also normal. What the issue probably is, is the gauge itself is innaccurate.

 

The gauges are inaccurate but I've never know one that was working to be that inaccurate. That's why I want to know his RPMs which should be around the 650-800 range when coming to a stop..but even then that low of psi for the oil isn't normal. The rising as the rpms increase is normal though but it dropping so low to a stop is not. I'll test mine today and see if mine does the same.
I'd try what Cam said and try a higher viscosity oil first. Something like 10W-40. I wouldn't go higher with the number in front of the W with winter coming up.

 

Drove it to work today and not a single problem. It dropped down at idle, but just below half. Drove home and the psi stayed slightly above half at crushing.

I'm not to worried, I'm planning a new engine build(have been since i got the car).