Oil Pressure

i have no oilo pressure when i start my 98 blazer but the oil pressure on the guage goes up when i turn the car off is this simply a oil sending unit or oil pump. i was also told that if the oil level rises while it is running that the oil pump is still working and the oil level does rise alittle so im hoping its just the sending unit i just wanna make sure hopefully someone here knows for sure.

If there is no oil pressure on startup, there should be lifter clatter, rod an main bearing knocking, and eventually it won't start.

Verify the indication of the dash gauge by temporarily connecting a mechanical oil pressure gauge. There is a very good chance that the pressure sending unit is failing.