Came back here to say; you called it right on. I apparently botched the valve adjustment (didn't tighten the nuts hard enough) and they must have gotten loose and went out of alignment. 6 out of 10 had been far too tight. Great call.

(since it was night when I tested it, I couldn't judge the smoke well enough, but power is more than enough to go up a steep hill at a good speed & vacuum gauge is very steady. Massive difference)

Also, I'd like to add to any who had this happen: if the top nut actually slips out while you're trying to adjust the valves.. compress the spring (and lower the valve) with a large and long hex wrench or something and try to side it in to screw back on. Might be obvious to some but others may need to know at some point in the future.