The P0500 code is telling you there is something wrong with the vehicle speed signal. It could be the sensor or the wiring. This MUST be fixed to make this work again.
I wouldn't say it shifts at the wrong time but it does sometimes from 1st to 2nd...Its the speedometer (psom). .the microprocessor are terrible in the speedometer as long as it has a digital odometer. They are famous for going out. Had to do it on both my trucks. Sometimes it would shift great sometimes it wouldn't. The microprocessor reads how fast the truck is going from the vss and then communicates with the computer on when to shift. The truck doesn't know how fast its going then trans goes into limp mode to not damage itself. Really hard shifts and at wrong rpm's?