I disabled airtime fairness, 802.11ac beamforming & 802.11ax/WIFI 6 Mode. This time, I reset it & didn't mess with any wireless settings. Basically named the networks, put passwords on them & left everything else as is.
Lesson learned. Don't read too many FAQ's & posts until you have issues! After resetting, I added two nodes and it has been rock solid for past 24 hours. 40 devices connected, no dropoffs from nodes or devices. Even Nest Protests stay online now...That has been an ongoing battle with the GT-5300.
Only been about 24 hours so I will not claim total success yet but so far, it seems to be working great.