1999 Suburban oil gauage falls

My oil gauge is falling to almost zero mark when I accelerate from a stop. At idle, it registers fine, while driving it registers fine, after I stop the gauge will drop when I start to accelerate. It will stay low but pop up to normal at about 15-20 miles an hour. If I stay at a low speed it will still pop up pretty quickly. When this happens the check gauges blinks. It is a 1999 Suburban with 135000 miles. The oil has about 3500 miles since the last change. What could cause this?