Transmission slip

[Deadbuck]

My 21 seems to slip from 1st gear to second gear. It only does this 1 time when it's been sitting. Then seems fine. Anyone else have this problem?

 

[flan]

Could be the torque converter drained back into the pan and hasn’t completely refilled yet. I know on occasion if mine sits for a while they do drain back. I go to put it in reverse and nothing happens for a few seconds until the pump in the trans refills it.

 

[Thompsre08]

Did this ever get figured out?