OD light flashing
I have on 06 and it started doing this. Son works for Ford on the computer end. We spent some time logging data. What this means is erratic lockup and or converter slip. In my case it only occurred at around 40 mph in OD. The converter would lock and unlock getting an erratic signal from the ecm. After three tries, the converter will lock out and the light will start flashing.
Okay off to a trans shop. They put in a new converter and control valve which is a likely suspect but did not fix the problem. He tore the trans apart and really couldn't find anything. Then he tore the filter apart and found part of a gasket in the filter. It turned out to be part of the gasket on the pump (I know little about the internals of an automatic). In looking at the flange the pump mounts on you could see a groove where it was not properly machined. He sent it out to have it remachined and put it back together. It works, but I am not real thrilled with the upshifts particularly 2-3. They seem a little sloppy. He claims it is okay.
Anyway I bought it used and no warranty.
As was said, this is an elusive problem and could be just about anything, but it is related to erratic converter lockup. Son checked with the techs at Ford and they said it is not a common problem (that figures).
At any rate it will take a real competent shop to diagnose and fix.
Good luck.
JU