Hello I have a 1997 Freightliner FL60 with a Cummings 5.9 2 Valve. At low RPM and low throttle settings it is smooth. At around 1500 RPM while acclerating the engine starts to miss and blows heavy white smoke from the exhaust. If you let up on the throttle to partial throttle setting the engine smooths out and smoke goes away. It is not using water. Turbo seems to be operating. Please advise