I have an early 99 that is just acting weird.
At WOT, it shifts great.
Normal driving to mild driving, also shifts great, until overdrive. When it drops into O/D it does fine, then once you accelerate another 10ish km/h it will jump in and out of O/D. 1700rpm to 2100 to 1700 to 2100 and continue until you either let off, or give it more.
I have a DP tuner, does this on all tunes except Tow, which I find interesting.
Also might be temp related, I have a temp gauge on order. I find it happens more if I've been cruising on the highway for a period of time, then have to do a stop and start in one of those tiny towns and go back to highway speed. If I drive around in town a while, then go on the highway it doesn't do it, regardless of tune.
Also the colder it is the more this happens I think ( I'm talking -20C and below).
Never noticed a flashing OD light, even purposely made it happen to watch for it. I'm going to pull the tuner tomorrow and go for a drive.