95 Mitsubishi Mirage 1.8 - Oil leak at high speeds only

95 Mitsubishi Mirage 1.8 liter 105,000 miles. The oil mostly leaks at high speeds or when the car is working hard. At 70mph all the oil will leak out in about 150 miles. When I don't go on the highway it barely leaks at all. I smell burning oil when I go fast or uphill.
There is no smoke coming out of the exhaust or under the hood. When I look under the car I see oil dripping down the oil pan and pretty much on everything else near the engine.
I had the valve cover gasket replaced and I replaced the oil pan seal (no gasket available for oil pan). Neither of these had any effect. If anything, the problem has worsened.