Well, I spoke with a gentleman at the tranny shop and they say that by just changing the fluid, all 14-16 litres and putting in a new filter, the symptoms are more likely to get worse and the tranny will actually start to slip, not shutter as it is now in Over Drive.
They are running some diagnostics on it now, will let you know the outcome and what may be needed but it is not looking good.
Maybe I will just live wit the shutter for now and wait until she blows the gears if a rebuild is evident in the future..... | 
