No 2nd gear

Ran the car tonight. Best 60' to date. 1.600. Bang 2nd gear and feels like neutral! Hit drive and pulls like a freight train. No leaks. Not hot. Fluid full. Drive it home and stabbed it a few times in 2nd gear and feels fine. Not even sure where to begin. It only under full throttle 1-2 shift. It's low band apply forward pattern cheetah manual valve body with 4500 rpm dynamic converter.