Thanks. I'm running Windows 11 on a big machine (20 core, 4.5 GHz). This could easily be a windows problem because windows received some updates around the same time. This is irritating, but not a showstopper.
It seemed like I had the same problem with switching tabs on TCMD v28 on Windows 10 Pro. I don't seem to have that problem on Windows 11 with either v28 or v29, but I'm having a different problem (see post about Take Command crashing under Windows 11).
I installed Windows Terminal -- and it seems pretty good. At least tab switching is fast like I was used to. Like you, I started with 4DOS, later 4NT, in the early 90s. I even have the spiral bound manual around here somewhere.
I may try Windows Terminal and tcc for a month but would rather use tcmd/tcc as a one vendor solution. I often have 5 to 10 tabs open in as many directories and switch between them often so a one second delay is noticeable, but not a show stopper.
COMSPEC is a red herring. The time to change tabs is proportional to the number of tabs jumped. For example, if I have 10 tabs open the time to jump from tab1 to tab10 is much longer than from tab9 to tab10.