Well I stopped early at a dealership in nortern Cincinnati area and two service writers came over and "diagnosed" the problem as possibly/probably the duovalve. Neither of them were concerned over the temps north of 80c, said it seemed very normal. We are now in Knoxville and temp gauge has been very consistently running ~ 90c.

The remaining issue is the cool air that comes from dash vents as we come to a stop. Although it's getting warmer further south we go so it won't be as much an issue - I hope!

Thanks for all the replies and will keep you updated...

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Dale