Brian,
I'll share a couple of experiences I've had with this and another fuel delivery issue and what I did to make the problems go away.
Our 1960 300F was acting pretty much like you say at speed. Although I'd changed the fuel filter, I did a replacement again and that problem went away. Just because it is a new filter doesn't mean it is a good filter.
Second issue may relate more to your issue. Our 1955 NYer T&C and terrible starting problems so my friend, Ken Brody and I started looking. When the car was idling you could see bubbles in the glass filter bowl on the WCFB. We removed the ceramic filter from the bowl and started it back up which had been a MAJOR issue until that time. From that point on I left that filter out and never experienced another issue.
Now I'm sure some will say you need a filter and I agree with that. We installed an electric fuel pump close to the gas tank for assistance on starting when the wagon sits for long periods of time. That pump came with a metal inline filter, so we resolved the filter problem.
California has expensive and crummy gas so that is another issue we deal with, and these changes really helped us. All of our Chryslers with exception of one have an electric pump with an inline filter. Someday I may install one in our 1953 Imperial Newport, but that car has never failed me for starting and fuel delivery.
Hope this info will be of some assistance,
John Lazenby