Tranny problem 1999 Sable, no replys on Sable board.

[JimLev]

I was on the highway doing about 75 and then got off onto a country road doing about 40 MPH. The O/D OFF light started to flash on and off, but the car drove and shifted fine. (it did shift into O/D)
I had to stop at a store and when I restarted the car the light was off for the rest of the way home (15 miles). I called the dealer (svc dept) and he said he didn't have a clue, didn't know anything about the light flashing. Got the usual, "if it does it again, bring it in".
There are no OBDII codes, the car manual and Hayes manual don't mention the flashing light, but it must have been flashing for some reason.
Today I changed the tranny fluid and filter, but this probably isn't the problem. (car has 53K on it). I drove it around and the light is still off, anybody know what the flashing O/D Off light is for?
Any help would be appreciated.
Thanks in advance.
Jim L.