Oil Pump or Oil Sending Unit Sensor?

its a 97 sport with 200,000 on the inline 6 and today when i left work at idle there was no oil pressure showing on the gauge. and the check gauges light was on. as i drove the pressure moved up on the gauge but didnt read full pressure. i checked the oil level and it was full. could this be the oil pressure sensor going out or my oil pump? and if oil pump how hard is it to change?

Tuesday
eta this is oft discussed here try a search
it will tell you to put a guage on it to verify pressure is still zero check bearing, pull valve cover ect rebuild motor or replace with donor

I would do 1 of 2 things.. pull the sender and check with a mech. gauge to confirm correct pressure, and go from there depending on situation. OR, just get a new sender (under 20$, I believe) and swap it in and see if it makes a difference.
Oil pump requires dropping the pan.. unless you have a lift, then you will have to un bolt a lot of your susp. But is easy enough if you are mechanically inclined.

Just had the same problem with my new XJ I just bought. X2 on the check the oil pressure with a gauge and replace the sensor. A new sensor for me was only $7 and 10 min of time putting it in. Unfortunately in my case, it turned out the be a cracked head leaking antifreeze into the oil which wore down bearings on the crank.... new motor time!!!