Low,fluctuating oil pressure on 1993 blazer 350cid

Did you try replacing the oil pressure sensor? Are you having any unusual noises from the engine or loss of power?

do you change oil at recommended intervals when the engine runs at higher RPM's it's normal for oil pressure to increase while driving

no,,, fluctuations mean =low oil pressure,oil level low,oil old or too thin viscotly,oil pump loosing or not develloping the correct pressure
pressure release valve spring weakened

I assume from the year it has high mileage. With mileage comes wear in these engine's bearings allowing oil pressure to drop because of the excess clearance between cam and bearings, also the crank and bearings. When the engine is hot and idling the oil is thinner and goes by the bearings quicker. If you have good oil pressure while driving, I'd leave it alone, maybe use a thicker oil or some lucas additive. My 89 does the same thing sometimes in the summer, but don't remember it doing it this summer. I use Mobil-1 and an AC Delco filter.

Of course you realize that the pressure fluctuates according to your acceleration right? If it's going lower than it normally did than there can be a compression problem with the engine or possibly the oil pump is putting out a low output.

oil pump might be going bad

DIAL IN CAB COULD BE AT FAULT, NEED TO GET ANOTHER DAIL GUAGE AND CONNECT TO SENDER, IF SAME COULD BE SENDER, IF STILL THE SAME, PRESSURE VALVE IN BLOCK STICKING DUE TO DIRT OR U/S, OR AT WORSE !!! ENGINE WORN, THIS WILL BE CONSTANT IN MOST CASES, FAULT IN GUAGES ARE NORM INTERMITANT.
LOTUS

center back of motor behind distributor..bulbous

nothing ..normal low pressure at idle while hot ...but really should be thinking fresh oil change and filter soon..also what are the RPM's at idle hot in gear with A/C radio and other accessories running?