Interesting...I too had "shift shock" or very hard downshifts from my Auto-3.6. However as my mileage has started to increase, it seems like all of sudden it has stopped. Also I still have very low mileage so figured it needs some time to break-in.
Currently the hard downshifts have disappeared. I also have tried to brake more gradually and that has helped.
MPG are not that that great...but I love the juice of the 3.6, lots of power.