1957 evinrude big twin 35 coming out of forward gear

[eolsen]

There is no play in linkage, up or down through the exhaust window. If I don't use the control box n cable and just shift manually on the motor I don't have the problem. Wouldn't that tell me the clutch dog and forward gear aren't worn? Also, I have replaced the cables with new ones.
Any additional thoughts? It usually only occurs in the first couple minutes then I don't experience it for the rest of the day.