After seeing your post, I spent the weekend and retested my other cars more extensively. After an initial minimal loss the pressure held steady on both my Subaru and 15 4R.

I decided to retry the 96 4R, and started to loose pressure a lot faster than the previous time I tested it. I walked around to the passenger side and there was a puddle of antifreeze on the found, leaking from the rusted hard line running to the rear heater.

I clamped that off those lines and re-pressurized and the pressure help stable for a several hours.

I'm not exactly sure what to make of it.

Perhaps I did the test incorrectly the first time or pressure leaked somehow w/o a lot of coolant. How?

I'm going to shunt the rear lines and retest. Hopefully those rusted lines account for the coolant loss and the misfire is a separate issue.

This is true of both of my 4Runners. The delta on my 15 4R was 100° and the lower was practically ambient. The Subaru lower hose was a lot warmer. I need to be more careful applying some of the YouTube general car advice.