Without a proper scan tool that can talk to the transmission control module you are sort of stuck. If both transmissions act the same way it almost has to be in the electronics and the testing of those requires a scan tool to read the signals and test the controller. You might want to check the connections and wiring and test the transmission range selector using the charts below. The first shows the connector pin view looking at the end on the selector, the other chart tells you which ones connect in which position. For that test you only need a continuity tester to be sure the switch conducts properly.
Images (Click to enlarge)
Monday, July 31st, 2017 AT 1:14 PM