2003 Windstar transmission problem

I have a 2003 Ford Windstar, 6 cylinder w/ 107K miles. Driving home about a week ago, my engine sounded like it was 'revving up' when I tried to accelerate. Checked transmission fluid, was fine - no odors, no check engine lights - but all gears seem to be 'neutral'. I have it at a shop now. It's been hooked up to the computer & nothing shows up as wrong and there is no external sign of damage. The linkage appears ok. Help if you know of something. I am getting ready to pay big bucks once they open the transmission.
Thanks