I have a 2003 Ram 5.9L Magnum. One day I went to my local gym to go workout and it drove perfect on the way there. When I got back in after my workout to come home I turned the key and before even starting the truck the speedometer began acting up jumping everywhere randomly. 30 seconds after starting the truck I got a check engine light, abs light, and parking brake light come on at the same time. The code I'm getting is "P0720 – Output Speed Sensor Circuit Malfunction". The speedometer works perfect as soon as I get moving, but as soon as I stop it will start jumping again. I also noticed the transmission shifts funny when taking off, almost feels like its trying to take off in 4th gear and then finally shifts to 1st. It shifts fine while moving.
I replaced the speed sensor on the side of the transmission, but the problem did not go away.
Example While Parked: