I have a 1993 7.3 IDI Ambo. 40K miles. Flashing O/D light. then it went away. Then it came back driving through hills. I pulled codes. (By the way, the ECC-IV "Lone connector to ground & check engine light is much easier than the other bulb method". Codes 62 and 67 were confirmed.

Code 67 - Removed connector shield and a cubic yard of gravel was liberated. So much, I have to use contact cleaner and compressed air to be able to push in on the connector locking button which apparently has grit packed into it. Upon inspection, the female connector sockets had oil or ATF in them. I cleaned it with contact cleaner but suspect the seal on the solenoid board is weeping ATF into the connection. Could this cause a fault?

Code 62 - will check gear select sensor tomorrow.