If the fail safe check ball is in place.. the minimum setting on the cable is important. If the minimum setting is not set correctly the check ball will seat and the trans shifts late like WOT
Have you checked the governor plastic gear to see if the gear is broken or worn out? Governor not turning, the trans thinks it is not moving = no shifts
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.