I just got my freshly rebuilt transmission back in my car and went for a few test spins yesterday. I was worried about the transmission because it wouldn't shift to third. Then I realized the speedometer wasn't working. I know the pcm need mph input to know when to shift. Could this be why I can't get the transmission to shift to third? Also, where should I start on diagnosing the speedometer?

 

Perhaps too obvious, but...
Make sure the correct VSS is installed in the tail housing and the cable to it is plugged in.