Rapid and excessive talking are considered to be symptoms of mania/hypomania. Is it worse since adding the Strattera? Gradually getting worse? Antidepressant induced mania/hypomania? Another tip off is the grandiosity -- he believes what he has to say is so important he can't not say it.
I suspect that a behavior plan won't work. If it is Strattera caused or fed, it's an uncontrollable compulsion. No matter how much he might want to stop, he won't be able to for any extended period of time....at least not until he crashes.