Have you scanned the vehicle?
What is the history on the vehicle?
Mileage, recent trans repair work or service?
If the speed-O ias not working the system does not knwo the vehicle is moving... since you say the speed-O works, there is another test
You can unplug the trans connector at the case or remove the trans fuse in the panel. This will put the trans into default - fail safe mode. The trans will then be in 3rd gear and would not want to move from a full stop without lots of throttle applied.
That will at least tell you the 3-4 clutch pack is good
In manual 2nd gear, the trans is not in 2nd gear?
Yesterday is history.