My truck normally did not use any oil since new except in certain conditions.The condition I am referring to is when cruising at 60 mph or faster in fifth gear and pushing the go peddle down enough to cause the tranny to drop into fourth gear,thus a sudden increase in engine rpm and a huge smoke screen behind me.These episodes will drop the oil level a notch on the dip stick every time.Yet I could pull the fifth wheel trailer or run empty at high rpm with no oil consumption as long as I do not get that sudden 2000 rpm jump up to 3000 rpm.I have started out from a stop with the tranny set in second gear and run the rpm up to 3000 rpm with no smoke period.Air filter is clean and fuel filters are changed at 10,000 mile intervals.I use Delvac 1 5-40 oil.Last oil change I had the oil analyised with an excellant report.No oil leaks from engine.Now at 39,000 miles the oil is dropping a notch on the dip stick every 500 miles with out an episode of the sudden rpm increase.Oil is checked weekly after the truck sits overnight in shop.A normal week of driving takes me 500 miles at mostly 70 mph and usually accelerate moderately getting an upshift at 2000 rpm.The truck seems to run good with fuel mileage consistant at 20.4 running empty at 70 mph.Is there a possible problem with the turbo seals?

What happened?

Dropped the oil and filter,went back to Delvac 1300 series in 15-40 weight.Just drove over 540 miles and used no oil,but did not kick her down to get the sudden increase in rpm.Do not know for sure why it started using oil on a regular basis,had run the Delvac 1 6500 miles on previous change with no oil consumption but the last one I dropped the filter at 6000 miles adding oil to fill it up again planning on a full change at 10,000 miles.After that it started using oil on a regular basis.I do not think the turbo seals are bad,would have bigger problems than I got.