I got a Vectra C with 2.2 L engine and AF23 automatic gearbox
I'm facing the following problem:
after driving the car for long distance or if being stuck in traffic the gearbox shift become not smooth at all
I've been told to change the transmission oil
Can I use dexron 6 oil?
I just want to drain oil from gearbox and then re-fill with 3 liters
please advise

one more thing my car is made in 2007
and only covered around 70000 KM