It's not really a matter of how quick/slow or when it downshifts as long as it's smooth. When I had the problem of 5>4 downshift, myself and others in the car, thought we got rear ended. It's that clunk/jolt when downshifting. Kinda like a bad shift when driving a manual where don't blip the throttle and release the clutch to quick.
Given that, programming could still be a root cause but after X miles of bad shifting due to programming issues, is there physical part damage as a result.