Well finally got truck back with trans serviced, temp sensor changed and replaced cooler line that had slight crack and leaking

Trip from Indy to Louisville last night hauling my daily driver in 24' hauler

Tried to stay on cruise @75 mph but even when off was over 60 for most of trip

Crossed my fingers and converter stayed lock unless I tapped the brakes.

So a 27.50 part might have been the problem

Thanks guys for the suggestions and hope my next trip is uneventful.