Automatic -When car has been driven 15 min or so and parked and sits for 5-15 min - put in reverse, when your touching break to stop the car has a strong jolt and loud thud in rear. Feels like you hit something. Put car in drive and as it automatically shifts - a very hard shift and that jolt as you go faster - notice the RPM needle jumps a bit. Once on highway and car driven another 20 all fine. Park in garage and in the morning - reverse is fine - this is intermittent - once every week or 10 days. Fluid was changed @ 110K or so - car has 163K.