Mercon ATF (Ford type) has an additive in it I was told years ago. ATF is designed to help friction materials grab one another where oil is to help them slip. It's not extreme but more coarse than engine oil. This is probably why the mythe started in the first place, thinking it would clean carboned up engines.
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!