I have a Chevy Lumina LTZ car. V6, 3.8lt engine. When engine temp is hot, it jerks while shifting through gears. It does not happen in winters and when engine is operating at normal temperature. It only cause jerks while shifting through gears when car is running hot e.g. after a number of stops at traffic lights etc. Can it be a transmission problem and if yes, why it does not happens all the time? I have already got the transmission oil and filter changed. Please advice.