Ford F-150 (2004-2008) :: Engine Revs Up Then Engages And Slam Into Drive While Decelerating?

My truck is a 2004 (new body style) 4.6L XL Supercab 4x4, trans code A, which I believe is the 4R75W transmission. I bought the truck used last year with 110k miles on it and it still only has 115k now. I think the problem with the trans was there when I bought it (it's highly intermittent) which may be the reason why the PO traded it in, because the truck is in excellent shape and has clearly been well cared for in all other regards.

The problem only occurs after having let up off the accelerator pedal for a while and coasting, then getting back on the gas without coming to a complete stop, like one might do coasting downhill or coming up to a light that turns green before you come to a stop. When that happens it feels like the transmission has shifted into neutral and the engine revs up freely for a second or two and then suddenly engages and clunks / slams into drive. This doesn't happen every time that I attempt to reproduce it, and it went for the entire summer without doing it once. But, now that winter is coming on in New England I find that it is doing it again once in a while. The problem seems to happen whether overdrive is engaged or not.

I've checked fluid level and condition and both are fine. Nice bright red color and no burnt smell. The transmission works well in all other ways except for this one issue. With the exception of this problem it seems to be engaging, driving and shifting perfectly, with no slipping, even when giving it a good romp, with or without 4x4 engaged, or even carrying a heavy load, causes no problems.

To me, this seems like a control problem of some kind, doesn't it? If it was mechanical or hydraulic I wouldn't expect it to only occur after coasting for a while.