Don't know if this will help or not, but the same thing happened to me a couple of years ago. I traded in an old Geo Storm for a Geo Storm GSI a little used with about 30K on odo. On the test drive car drove fine. when I drove the car off the lot and up a hill and I had to downshift, the car wouldnt go into gear in any of the gears until I came to a complete stop, and I finally got the car into gear and took it back to the dealer, the dealer checked the car out and a nut had come loose and bounced around in the tranny and screwed up the syncros, at a dealer cost of about $1800.
