[cadillac_al]

If it was mine, and the trans was getting full vacuum, and a new vacuum modulator makes no difference, I would buy a Transgo shift reprogramming kit. When replacing the springs in the valve body valves I'll bet I would find a stuck valve even though I have never seen it happen before. Maybe it has a stuck or broken spring. I still think it will be something simple when you find it. just my .02