1996 Ford Taurus transmission will not shift out of 1st gea

I have a 1996 Ford Taurus. The transmission shifts properly through all gears when the car is cold, or has not been driven for at least 40 minutes at interstate speeds. The first note I would like to make is, the speedometer isn't working, but hasn't worked for 10,000 mi. I noted this because I saw a post regarding shifting and a possible speed sensor. When the car has been at interstate speeds for about 45 minutes, and then driven in town, the following happens. The transmission will stay in first gear well over 4000 rpm, and then either, 1- shift abruptly with a good stiff shift, or 2- will not shift into 2nd gear without keeping the high revs until it does shift, some times letting the engine run away, in between shifts, (from 1st to 2nd gear only). Shifts are always crisp and in the proper rpm range until the highway drive is done and stop and go traffic is encountered. Any help would be appreciated. Tom.