Tomorrow I'll do some further checking and temp measurements per your advice (bottom of radiator versus top, checking the lower hose (I did put a spring in it last year when I realized it was collapsing when it ran), and I may just pull the thermostat out to see how warm it runs without one for a bit...

And to answer the question about how I was driving it.. I was doing about 50mph on long open stretches, with outside air around 35 degrees F.