Have the tranny flushed ASAP!!
This is not something for the do-it-yourselfer, as a true tranny flush will get all of the tranny oil changed, not just the 50% or so that is in the pan. As stated above, this tranny needs Mercon V for a reason... Try a dealer and expect $160 if they don't have a deal going. An oil change place might be ok, but they need to use real Mercon V, not III with some additional additives, and they need to do a real tranny flush, not just dropping the pan.