91 Crown Vic stuck in first gear

Hi
I have a 91 crown Vic with a 5L and 4 speed auto, it's been sitting in the garage for 3 years, tried to take her for a drive the other day and it won't shift out of 1st gear. It's got a lot of miles on but has never had this problem before. Trans fluid was changed around a year before I parked it, any ideas? I need to get this old girl back on the road again.
Thanks

You may need to let the car run for a while to get to top temperature. The car SHOULD shift from first to second at about 40 mph. Take her out and run the snot out of her, after fully warm. If she does not shift at 42 or 43 mph, you have a problem. This will not damage the engine. You may have a stuck vacuum modulator.

Have you tried to start moving the car from a stop in second gear ? As far as I know, Fords are the only vehicles out there that will do this. Sometimes known as the "snow gear", reducing torque to the rear wheels in slick conditions. If you shift to "2", and the transmission still remains in first gear, replace the vacuum modulator. It's easy to get to, and pretty inexpensive. Make sure that you have no cracks in any of the vacuum lines. Just spray a little starting fluid around the vacuum line. If the engine revs up, you have a bad vacuum line.

Best wishes,,,