Atani: Thank you for your comments. I look forward to looking at your ESP32 CS project when I get some time in a few weeks.
How is the fit on the Deek Robot board? I take it the Arduino shield has the longer pins and deek does not? Do you just leave it pressed in 3/4 of the way and hope for good connections? Did you snip the protruding pins from the output connector to let it sit that much more flush against the Uno/Mega power connector? Normally, shields bottom out in the Uno and the exposed 1/8" of bare pins is fine, but this board would only bottom out if it sat flush, which it can't because the USB and Power connectors are in the way. Or it sits angled with the end towards the power side of the Mega sticking up in the air
Also, are you heat sinking the chips? The metal slug is under the chips, so best you could do is try to clip something on to what little metal sticks out the ends or use heat transfer tape and a heat sink and hope for the best. How much current would 3 n-scale locos draw? I imagine since we only use one chip at a time, we would put in 15v and get out maybe 14v with the voltage drop across these poor performing chips? And maybe only 1A or less before it shuts down? I think this is accounted for in the DCC++ code since the default is to shut down at .8A before the chip does.
