Changed Transmission Filter, gasket and ATF and now my transmission sounds different?

[chugach]

So the gasket was leaking and Im sure the ATF was pretty old. Yesterday I drained the pan, replaced the filter and renewed the gasket. I filled it with DEx/ Mercon ATF. This moring when i started it there is a new sound to the transmission. It has a low dull knocking sound. Is that ok? Does the Dex/Mercon have different propertied than original DEx II that is says to use. Or should i switch to someting else? I do not want to ruin my tranny. The van is a 1994 s/c alltrac.

[Ace MM]

I've had very good luck with Castrol transmax high mileage fluid in my low mile hiace.
I would do another pan volume change with it and see if it changes anything. I did 4 of them.
Once I did a full machine flush with the Castrol, it still took about 150 miles for the problems to stop. They have not returned after 2 off road trips.