I have exactly the same trouble - oil pressure started going off the scale this winter and is getting higher, even though the weather is warmer. NOT the sender or gauge, I've checked with a mechanical gauge. Also changed the oil, and filter, even tried a 5-30SAE synthetic.
Anyone know what this could be? It is a 1988 YJ with only 30,000 original easy miles on the four cylinder.
I'm thinking maybe pressure relief valve is jammed? Anyone know where it is located? (In the oil pump?) My factory manual is no help on that.