Actually, the accumulator SPRING is my favorite topic, while I don't advocate using the blocker rod I do recognize that it does firm the shift.

Since the rear servo releases through spring pressure only it can't release at the same rate as a hydraulic servo of near the same size can apply. Even if the buttmeter doesn't feel it, there is overlap if the servo feed is unrestricted. If you jack the rear wheels clear of the ground and manually shift from 1-2 at around 1500 rpm you will most likely see the rear wheels come to momentary stop due to the overlap.