fresh rebuilt 4l60e wont shift to third
Inspect the External Wiring, Internal Harness and Solenoids...
The abnormal Speedo behavior in addition to the Failure to Shift Up to 3rd-Gear would direct me to look for an Electrical issue First.

You should try and get a hold of a Scan Tool or Software that can Read Transmission and Body DTCs for Open/ Alter. Circuits.








