OD light flashing on my E4OD transmission

[LLM1250]

My 2000 F-350 V-10 4x4  Over Drive light just started flashing last week.  The vehicle has 90,000 miles on it.   I just purchased it 8 months ago, so I'm not sure if the fluid has been changed...any ideas on what I should try first ?

I took it to Oreilly's Auto to have the codes checked.  My codes are :

                                                                                                               P1000

                                                                                                               P0783 

[Moses Ludel]

LLM1250...Here is the CliffsNotes version of the P0783 Code:  P0783 FORD - 3-4 Shift Error...Read more at https://www.autocodes.com/p0783_ford.html.  You'll find a nice website for quick referencing DTCs.  The P1000 code would be incidental, it has more to do with code reading and clearing.  This could be created by the AutoZone read.

I would do a TCM code read before replacing any parts.  That could narrow down your possibilities.  The transmission controller is key to pinpoint diagnostics.  The P0783 code simply provides a ballpark range of potential faults although you can use this DTC/P0783 as a troubleshooting place to start.

Moses