both valve bodies could cause the same problem for different reasons. That said, I would suspect a governor valve or kickdown valve stuck or assembled improperly. Are both vbs later model that match up with the case in the area behind the accumulator? Maybe the first vb had the kd spring on the wrong side of the valve, but the second valve body wasn't a match to the case and bled pressure. Check the date code on the second valve body and see if it isn't around late sixties.
