I received a Craftsman LT2000 (20 years old) freebee that had the same issue.
Transaxle had to be disassembled and thoroughly cleaned, regreased, and resealed.
It now runs and shifts beautifully.
I've had success spraying Liquid Wrench penetrating oil in the areas where it shifts and work it back and forth to free it up. That being said, not sure what craftsman you have exactly. So many different models.