<VV> low oil pressure?

[Trey Bosson]

recently but not always,the gauge on the dash,shows almost no readable oil pressure, oil level is at the full line. have driven it several miles with gauge showing this reading. engine sounds fine, at last oil change 2500 miles ago Ididnot change the oil filter, could the filter be causing this false reading. its a 1986 305 v8 with probably 400,000 miles , would changing the oil filter remedy this,  trey bosson  wellsville ny   60 v8 vair