Started a while back and comes and goes. Only commonality I have found is the truck needs to be warmed up for it to happen and usually after a few hours of driving. The downshift from 5th or 6th into fourth, at times, produces anywhere from a light to violent clunk, feels like a typical tranny slip. It will do it while in cruise and it will do it if I don't have the cruise on. Can't figure out if it is going to be a tune issue or hardware. It does it only downshifting into 4th from 5th or 6th, no other downshifting is a problem and usually the 6th to 4th produces the worst results. At highway speeds that is usually a shift from around 2Krpm to just over 3K rpm (6th to 4th) if it is from 5th it is about 2500 to 3K. Start from a stop and go WOT and there are no issues. Having it in Tow/Haul or not makes no difference as far as I can tell. IT can do it on one hill and the next time be just fine or do it 2-3 hills in a row. After this last trip it will do it at 9K feet or at 60 feet elevation, didn't make a difference there either.

Another issue that may be hurting the computer is the truck originally came with the 235 tires, it now has 285's and the rear is only 3.31. I plan on going with 265's and maybe still a gear change to 3.73's in the future. I usually only notice this on long trips, first was a 1500mile hauling an ATV, second was last week during a 2500 mile empty. Although I have had it do it a few times locally. I figure those bigger tires can't be good especially with that high of a rear for the management system.

 

my truck also used to shift reallly rough but then only first thing in the morning(kinda odd) ,got a software update done and that solved the problem
i'm pretty sure there is a TSB about this

 

Yeah I am finding out this is known and a reprogram may or may not fix it. I wonder if a tune from 5 star would be a good way to fix it, sounds like Ford hasn't totally figured it out and being out of warranty I don't want to spend thousands for them to diagnose and re-diagnose and do a bunch of stuff that won't fix it.

I do also have some poor shifting at low speeds, seems to hold gears too long IMO. Maybe I'll have them update with the latest flash, do a flush and go from there. When it shifts at its hardest, eventually there will be a gear or U joint fail at 65+mph.

 

the update costed me about $180 (with diagnosing)
worth a try i think
i got mine flushed and it didn't make a diff. at all