When shifting to drive from park or reverse I have the classic delay before the transmission/ drive shaft engages. It acts the exact same as my old 1980 F150 with the 300CID. I remember when the u joints went out on that truck and what I am experiencing now is the same. With this in mind, on occasion, if I need to pass on the freeway and I drop out of OD, every so often the torque converter unlocks, rpms rev up and then the tranny downshifts rather hard. In fact it will kick the truck forward if I am accelerating hard enough. Feels bad *** but I know it is not a good thing. The transmission up shifts fine. DO the U joints affect the vehicles ability to get into gear when down shifting or do they only come into play when engaging the drive line? What about the "slip yoke"? That may be the incorrect term, but could it be an issue as well? I have yet to replace the tranny or re-gear in light of this issue. The fluids and filter in the tranny were changed (full system flush) about 30k ago and it still looks and smells great.
Education is appreciated gents.

 

I had the same problem in a different Ford vehicle. Ford had to reprogram the trans in the PCM. Eventually a TSB was issued. In another Ford vehicle I owned, it was recommended to re-torque the valve body bolts. I found some to be finger tight. Trans worked fine after re-torquing.