Really need to dig further in to why the code P0700 is being set.
A P0700 is a problem with the transmission control system, which could be the valve body, the transmission control unit or the wiring harness.
The speedo spiking to 70 when in park may or may not have to do with the transmission. It could be the instrument panel or the speedo head. I would try disconnecting both speed sensors that you replaced and if the speedo stays pegged, then it is most likely in the speedo head, if the speedo goes down, you may have an incorrect speed sensor, a wiring problem or a 'freaking out' transmission control unit, which relays the speed sensor signal to the dash and other computers.