My initial though was that the trans may not be disengaging completely when coming to a stop. Doesnt take much for a piston in the valve body to stick. There should be some sort of connection between the engine a trans so it can tell where the throttle is but my knowledge of these trans is limited to looking at one as I pulled it out of my 59.

Your intake leak needs to be fixed first of all IMO where was it leaking from and what have you done to try and fix it?

Scott