Hello and welcome to the Forum. A flashing OD light means have the Tranny checked as soon as possible. If it didn't start until after the wires were cut that leaves you with, yes the Tranny needs checked IE a real fault. The other route means one of the wires that goes to a sensor the computer uses to check the Tranny is still open or you could have shorted a wire depending on which state throws a fault (I have not looked at a signalling schematic).
I can't remember all the faults that make the OD light flash, but some are:
Service Transmission Soon
Transmission Over-Temperature warning
Solenoid is going bad
Torque Converter issue/slippage
Bad speed sensor but this is normally paired with an erratic speedometer
With your number of miles, when was the last time you had your transmission serviced? I am a big believer in that if one is keeping their truck for the long haul then it is best to half the transmission service mileage. With the new service technique of using the old oil to flush and power clean the Tranny with highly filtered old oil, I have had good luck with not having any major transmission problems. I also use Amsoil Synthetic Transmission oil.
