Traveling home today on a 40 mile stretch of hilly road the transmission started to up and down shift mutable times like trying to find the correct gear to be in , shifted up and down at speed over 60 m.p.h. and then on a steeper hill when giving it more gas to get up the hill a cloud of smoke come from the rear of the car and could smell burnt oil ? slowed down to around 50 m.p.h. and things got back to normal. In town it shifts normal at low speed but when I accelerate it keeps up and down shifting . Can't find any oil leaks but can still smell burnt oil . What could be the cause the transmission to be erratic in shifting ? any help on this would be greatly appreciated as I need to get this taken care of.