truborich is giving GREAT advice here. Listen to him.
I have an incredibly well maintained 2002 EX that I had a transmission flush at 50,000 miles and unfortunately I didn't think of doing it again until around 110,000 miles. I NEVER had a transmission issue, as it got very little 4 wheel driving and this thing has never, ever been beat.
So I bring it into my local transmission flush service and after 2 and a half hours later...that should have been the first warning...the young kid says, "Ah Mister. The tranny ever slip before?" I said "Nope. Things been rock solid". As he's looking at his shoes he tells me "Well...it's going to now".
He goes on further to tell me...while there's four other customers in the waiting room..."Yeah, we've had several of these Explorers that we've done and almost everyone starts to slip after we flush the transmission." I was pretty civil about the issue (under the circumstance) but I told him that the ethical thing for them to have done was to have told me that before they even touched my truck.
Sure even, 2 miles down the road it started to slip. Brought it to a transmission specialist and the minute I told him it was an Explorer he wished me the best of luck and said these things were grenades. Less than a month later, the tranny was ruined.
Unless you have had the transmission serviced EXACTLY at the required intervals and had the dealership sign off on it, DON'T flush the tranny. You're asking to become $2,000 lighter if you do!