Thanks everybody, great info here.

No no visible wear on the teeth but noted above comment on this possibility. Dropouts are aligned properly on the bike. I am using a Campagnolo 10 speed chain that is still OK but near the end of its life - used it because it was available and the right length - and maybe that’s why I notice the problem more now than last year on the Tommasini where I have a low mileage 8 speed chain. I have a 13-26 freewheel on there now which will probably get me up the hardest climbs at Eroica but I’ll probably try the setup with a better chain.

Otherwise Im going to put the freewheel on my maintenance and tinker list to check out these other issues.