Well..
It could be several things. Just a few would be, 2nd gear band is smoked. Servo pin blew through the anchor. Band anchor broken. 1-2 shift valve stuck.
Does the car run up in rpm then shift at a high rpm into 3rd?
Sounds like a 2nd gear band issue whether it be band, servo pin, anchor on band or anchor in case. BUT you will find it to be a 2nd gear problem.
Bruce
We4