Pressure reg has nothing to do with the converter drain back, it's all in the manual shift valve where the ring closest to the link tab is, it is machined smaller than the rest of the rings which seal to the valve body, it allows fluid to escape converter whether there is a worn pump busing or not. The fix uses a valve with all the rings the same diameter to keep air from leaking into the TC. Old TQF's used a special valve and spring to control the converter, either a converter pressure reg or a switch valve depending on if there was a lockup or not. TQF's used in Jeeps were configured different also.
