Chevrolet Repair: oil pressure gauge goes up and down, oil pressure gauge, oil pressure sending unit

Question
I own an 88' Chevy Silverado 4x4 P-up truck.  It has approximately 96K miles
and is as strong as an Ox.  Periodically I noticed that the Pressure Gauge
jumps up and down from 30 - to 60.
I have been changing my oil as far as 5,000 to 6,000 miles.  I also been up
keeping my tune ups and checking and change the fluids when needed...
Why would the oil gauge be jumping like this?

I just Flushed my motor, changed my oil and filter.   The gauge is currently in
between 40 lbs.   momentarily it starts to jump up and down from 30 to 60
sometimes below 30...

Please help me ....  

Answer
Hi Mr Crabbe..... first is that a manual or electric gauge...if electric try changing the oil pressure sending unit....if manual check the line to the gauge for blockage....if electric sending unit ok check for intermittent short to ground...if manual line ok check the gauge....hope this helps