I try to do my fluids on it, but my Tundra was bought used with 73k on the clock, zero changes. Back then everyone griped about how WS changed color fast, so it must be crap... so I did a full flush, and it quickly was nice and red (I also decided to risk it with Maxlife). IIRC it was still nice and red with I did the job 50k or whatever later, still got a nice full flush.
My Camry, that had 140k on it, with who knows what kind of driving, was very dark. Dex III? No idea, but it was dark, and looked even worse as I drained it. Full flush. I waited too long, did something like 20k before doing another full flush--I saw quite a bit of dark / black material coming out, I presume clutch material being held in suspension, getting "cleaned up" by the new ATF. It's rather nice clean now, shifts good and hard at 5k rpm (probably shouldn't be doing that!), with only a cold start issue (have to wait for it to pump up, probably an o-ring given out), but at almost 250k maybe any failure is indistinguishable from wear&tear?
As to particulates preventing slippage, I don't buy that. Ford used to play with the fiction modifiers for shift quality (maybe all of them did), so garbage in suspension is going to... play with shift quality. Anything in suspension is going to find itself sandwiched between those clutches and metal plates. A D&F means you have reduced what is in suspension by some percentage, a percentage much less than 100% (to be fair, a full flush isn't 100% either, as there are piles of nooks and crannies for old ATF to sit in). Engine bearing surfaces are always (?) separated by motor oil, transmission clutches, I want to say get that oil squeezed out by what they do, as it's intentionally locked together by friction: and each time they shift, some amount of slipping occurs while the oil (and suspended garbage) is being pressed out.
And if garbage in suspension was helping it shift... as you do D&F's the transmission is going to start slipping, and quickly fail. Might as well hasten inevitable I say, and save on the cost of good ATF going down the drain.
*
Of course, I advocate one thing, others advocate another. I'm sure a careful search of the archives will show a great deal of people doing both, and both having good results. I'll bet, dollars to doughnuts, in many cases and very likely in this case too, either method will result in the same exact outcome: a transmission with fresh fluid and proper operation. That's my opinion in the matter.
