What will cause low oil pressure gauge to enter red zone after temp is above 190*?

Odds are the engine and/or oil pump is wearing out.
A weak pump can cause low oil pressure, as can worn engine bearings.
The oil is pumped thru the crank bearings, then up to the top of the cyl heads. The pressure switch is midway up the block.
10w30 oil is made to be used between 0 degrees and 100 degrees. As the temp goes up the oil is supposed to get thicker, but only so much. So as the engine warms up the oil gets thinner and naturally looses some pressure. Thinner oil will "leak" thru worn engine parts.
You may luck out and have the pump replaced and fix the problem, but if it has more than 125,000 miles on the engine, the bearings are probably failing too.