Eratic oil pressure reading

I have a electrical oil pressure gauge that i added to car due to ecb board problem with stock gauge. readout of 4.5 to 75 psi but i have needle bounce at 1400 rpm to 1800 rpm and if i let off accelorator it will show 45-65 depending on heat of car. i have never had lifter noise and run synthetic 5w30 oil every 3k . help, gauge fluctuates from negative to 55 range. sending unit has been changed 3 times and my mechanic says “whats up”

Install a direct reading mechanical gauge to get a true reading. Your electronic gauge could be picking up interference from many sources…

My mechanic has had his gauges on several times and all says okee dokee. Do you mean interference with the electrical impulse to gauge.? Mechanic is hesitant to install oil gauge that uses oil line tubing inside the cabin. Paranoia over a broken line i guess.
Call me cautious but i have yet to feel comfortable driving with this going on, even though there are no signs of oil pump failure. eg. lifter noise temp rise etc. Appreciate any help.