F350 OD light flashing

My Truck Is A 99 Ps/sd And Has 148k. My Od Light Just Started Flashing. The Truck Still Shifts Into Od If You Push The Button At 50mph And The Light Stops Blinking For A Couple Of Minutes. If You Stop And Start Off Again The Light Is Still Blinking But It Shifts All The Way Back To Od. It's Been About 12k Since The Last Filter And Fluid Change. Fluid Level Is Good. Any Suggestions?

Get the codes read asap. This could be as simple as the DTR (digital Trans Range) switch being out of adjustemnt, or the ATF being too hot.

Autozone will pull codes for free.

It can also be that the T/C is slipping too much, this is relatively common, and typically because the wrong ATF was used.

Thanks For The Advice, I'll Try To Hit Advance On My Way Home From Work. The Fluid Getting Too Hot Makes Me Wonder If Skimping For The Cheaper Fluid 12k Ago Was Worth It. Maybe Right Kind Wrong Brand.