So - making some progress. First, I checked my fuel pump and it was pushing <1/2psi and even less when it warmed up. It’s mounted about mid-tank level, so my guess is that when the tank was full, it got a very temporary pressure assist and it ran great for 30 miles or so. Swapped out the pump, and lo and behold - it idles better and has more power (go figure). And I did use my little balance snail, but the new pump has everything running better and my idle is now much higher so I’m going to go through it all again! Thanks gents. The story will continue….