My 98' SL500 started to act up while driving under load. It idles perfect and drives fine under light throttle but as soon as I push it a little it hesitates, it cuts in and out through the entire rev range. Coming to an almost complete stop when the tranny gets into 1st gear the engine will hesitate a split second and at the same time the oil pressure gauge bounces for a split second then idles perfectly. The car has 33,000 miles and has been a garaged kept. Any ideas or common issues?

Thanks