95 Explorer - transmission hates hills

[MyFirstExplorer]

My 95 Explorer with 150K miles doesn't like hills. Even the slightest uphill grade causes the transmission to surge into overdrive. Backing off the gas returns it to normal. Yes, the O/D OFF light is flashing. Pressing the button on the end of the shift lever does not disengage it. Is this possibly an electronic / sensor type problem rather than a mechanical (big bucks) issue? I'm dreading the thought of putting major dollars into it. Thanks!

 

[Vargas]

If the O/D OFF light is flashing, there is a trouble code that should/might point to the cause of the problem. Don't know if a conventional code reader will pull it or if you have to have a shop or dealer retrieve it.