So after getting back from the next door neighbor's house (I've been doing a small remodel job for her, she had some water damage over an entryway, had to replace the header and get wallboard up, tonight was tape and first mud coat) I pulled out a Kato SD40 and ran it on the HCD. There was one spot that it derailed a few times, and after checking out the connection, it was where the former owner had installed insulating joiners and the connecting tracks had gotten out of gauge.
I didn't like that so I pulled up the sections of track and laid down a piece of flex track to help the curve, and soldered both ends. One end the rails were up a tad, so filed them down a bit. The curve looks a little smoother and the joints at both ends look straight and flush. Once the glue dries (hopefully before bedtime) I'll test the SD40 again. It's a really nice running engine.