2 weeks ago AST (18)/ALT (49) normal. After surgery taking Tylenol (acetaminophen) (4 grams/day for pain. Levels now elevated AST (50) /ALT (163). Tylenol (acetaminophen) cause?

Not necessarily. Any number of medications used during surgery could alter liver enzymes. Tylenol (acetaminophen) at the dose you used is generally safe. The enzyme levels are not too high and you may wish to repeat these in about 6 months. In the meantime do not drink alcohol at all.