C-6 starts in 3rd, locked in 1st

Not in a 429-460 powered vehicle, but it's still a C-6.

I've got a 67 Fairlane GTA. 390, C-6. I was out fooling around today and romped on it just a little. About 3/4 throttle from a dead stop in "D" . It shifted what seemed like a little early. At the next stop sign it started out in high gear. No shifts. Does the same in "2". In "1" the car will not move forward or back. Locked trans, does not pull the motor down. Just like it's in park.

Drove it a few miles home. Each stop/start it was the same, starts out in 3rd.

Ideas?

I have rebuilt a sbf C-6 about 15 years ago, but have not been in one since.

It's working again. For now. In low the car would not move. It was like having a transbrake. Only had 3rd and reverse. Checked the linkage and then took it for a little drive. Started in 3rd each time then I slowed to about a 5 mph roll and then pulled the shifter back in low. It barked the tires for a split second when the wheels locked up and then it broke free. Appears to work normally now. I think it was either the governor was stuck or the 2-3 shift valve in the valvebody was stuck.

Hopefully it will get me through the rest of the summer/fall. Cruises, Drive Inn nights, etc. I will pull it and rebuild it, add a shift kit and a new converter. Was goignt o have to pull it anyway to replace the front seal. If it doesn't last until then I will do it when it goes.

all wrong ! the High? reverse clutch pack is done !! and it's locking the hi/reverse drum to the forward drum , take it out and overhaul
Frank