After some more fiddling around with the dec motor, I was able to get some pretty good guiding. Following are some notes on my experience. Some of this is standard advice from experienced users.
-The advice from ES and forum members available here has been invaluable. Taking the time to read, absorb, ask questions, and attempt to apply the suggestions has made the difference between barely managing 1 minute frames to getting good 5 minutes ones. There are no shortcuts.
-I had to tighten the dec gear mesh quite a bit to prevent a recurring dec drop (sudden drop in the dec graph of between 4"-8" that ruined the frame and was happening regularly) and then had to loosen it a tad after it starting binding. It took several attempts to get to this point. This is time consuming because the guiding result of any adjustment can only be tested outside at night. It is of course possible to test motor binding indoors but tracking a star is really where you find out what's good enough.
-The best guiding happened with high dec aggressiveness (85-95%) and RA aggressiveness between 40-50% and guide exposure time of 2 sec. But sometime 1" worked better to steady things if the corrections were too slow. Specifics often depend on conditions and guiding equipment.
-Standard guiding recommendations (E heavy balance, cable management, etc.) made a big difference. If I ever forgot to balance E heavy it was immediately obvious on the graph.
-Taking the time to polar align really well made a big difference, including checking and realigning a couple of times if I had reason to doubt it.
This was the first time I have had consistent frames more than 3 minutes long (I only had to drop 2 of 26 5-minute frames).
Scope: ED ED102 refractor
Mount: ES EXOS2-PMC8
Camera: ASI 1600mm Pro
Guiding: Zwo mini guide scope, ASI120mm-mini camera
Other: Asiair and tablet
Software: Pixinsight, Lightroom
Dark and flat calibrated
Scope: ES ED102 refractor, Celestron C8-N Newtonian
Mounts: ES EXOS2-PMC-8, SkyWatcher Star Adventurer
Cameras: ASI1600MM Pro, Nikon D7500
Lens: Nikon 200-500mm, Tamron 70-200mm G2, Nikon 120mm manual lens
Misc: ZWO ASI120Mini Guide Camera, ZWO 30mm mini guidescope, Stellarmate, Asiair
Software: Kstars, SkySafari, ExploreStars (android), Pixinsight, DeepSkyStacker, Regim, Astrostakkert, LR/PS, RNC-color-stretch
Computer: Macbook Pro, Surface Pro 4, iPhone, Fire 7