About a week or so ago I noticed my O/D light started flashing while I was driving. I depressed the O/D and it did nothing! I had to pull over put it in park and turn the truck off. Cranked back up and it was ok. Well yesterday it did it again not once but twice. I repeated the actions I had made the first time this happened. It worked each time. Saw on you tube it may be the speed sensor switch. Please if anyone can help with a possible reason I’d greatly appreciate it. I did call dealership and they said they need to run diagnostic first to see what the issue is. If it is the speed sensor switch then paying $125. for diagnostic is senseless. Please advise. Thanks in advance.