No help with JD interlocks but you could test a bit to isolate.
See if you have spark after it dies without the levers engaged. You could have a loose wire. It might be dying for a bad plug which when hot opens. Or a blocked gas vent which will kill the engine but start up later.
From your description the interlocks work, the machine runs then cuts out then will only start with the levers depressed. It does not seem like they are a problem unless you have a consistant intermittant which generally does not happen.