1999 Plymouth Voyager Speedometer/Transmission issue

1999 Plymouth Voyager Automatic

Roughly 75%(the other 25% of the time everything works fine right away) of the time when I start my car after it has been off for a long time(like when I get in it to go to work at 9, and it has been parked since 5.) I have some trouble with the speedometer. It will jump around, and sometimes will even max out. This problem has causes the car to shift iregullary, and the service engine light has come on a few times with a transmission fault code thrown. This period of the speedometer jumping around, and sticky shifting will last a few minutes(And sometimes I have to turn the car off to get it out of the failsafe mode where it will stay in second gear.) But eventually the speedometer will start working perfectly, and there is no shifitng problems(which is why I am guessing that the problem with shifting is tied to the speedometer issue). One strange thing is that I often have this problem in the morning when I am going to work, but it has never happened when I am leaving work. Does this sound like an issue with the vehicle speed sensor. Also do you know any reason why there would be an intermitant malfunction such as this.