chensley: Your old sending unit is on the underside of the engine, the passenger side of the machine, below the oil filter. It's black and about 1.5 inches long.
I've been having the exact same problem in a 91 Jeep 2.5 .
I replaced the sending unit on the passenger side right next to the distributor cap and the oil filter. But, the oil pressure gauge 'pegs out' on the highest pressure after the engine is running.
The Oil Sending Unit is new, but the gauges don't read properly?