1999 Windstar transmission

I have a 99 windstar with 136,000 miles on it, and I do quite a bit of towing with it. it has a trans cooler That i had installed about 20,000 miles ago because I was starting to worry about how much longer the transmission would last. The fluid has only been changed three times since 55,000 miles.
The other day my wife was driving it and all the gears except first and reverse went out on it just like it was in nuetral. I rented a code scanner from O'rielly auto parts and didn't get anything to come up on it. I was hoping that it was just a sensor or something easy. Does anyone have an Idea what could be wrong besides having to replace the entire transmission? Cottman transmission told me it would cost anywhere between 1900 and 2900 to replace it. They also said that it sounded like the seals went out in it.

Thanks for your help

The one fairly easy-to-do repair on the Winnie transmission "in place" is the first-to-intermediate servo. It will cost about $20 in parts and 1/2 qt of fluid.

If you pick up an exploded view of parts from the dealer parts counter it will slhow you most of what you need to know.

Also there is the TRS sensor that "tells" the powertrain controller which range you've selected.

I'm no tranny expert ... maybe someone has better suggestions.