I had two issues with my 5r55s. First time, I had a couple of instances at the track. After doing a run, it would hesitate before going into reverse in the pits. After cooling down for a while, it wouldn't go into gear unless I revved it up to about 4 grand, then it would slam into gear. The last time that happened was in October 09, last day the track was open that year. Replaced the battery at someone's suggestion. (it was time anyway, was cranking slower, but he said he had the same symptoms after running the e-water pump and fans too long).
The following June, out of the blue it wouldn't go into gear after a long highway drive, even with revving it. Ford ended up saying the gears in the transmission pump were binding, and thankfully they replaced the pump under my extended warranty.
Never threw any codes either time, but when Ford was diagnosing it prior to replacing the pump, I think I remember them saying the trans wasn't seeing the pressure that it expected to see.