Hello Todd Overheating can be a timing issue also. You could be slightly too retarded and the problem surfaced with the hills. Or your lever is in the wrong position (operator error).
Check the impeller, but I would think the rebuilder checked the status of the impeller as part of the rebuild.

Where Are You From? Tucson, AZ

Do You own a car built by Durant? 4

Thanks Bob. I hadn't thought of that as being a possible cause. I actually don't have the steering wheel controls connected in my car. When we rebuilt the engine and got all the bits run, we weren't sure exactly how to get things set up, so we got everything seemingly time right and ran it. That was close to 300 miles ago. I wonder if things could have 'shifted' out of time on their own?

It's been a few years, but as I recall the impeller was not in wonderful condition when reinstalled, merely usable. I guess I will do my diligence there and see what is found.
Thanks again.
-Todd

Where Are You From? Marysville Kansas

Do You own a car built by Durant? 1923 A22 Touring