Just an update to close out my observations for future reference:
I did find one reference to the throttle cable adjustment that I thought I would verify before I pulled the carb again. That was all good as well, a little loose on the go juice, and a little tight on the return cable..
Out of ideas, I took the carb completely out again and this time went after the vacuum chamber. Nothing visually wrong up top, so I just washed the slide and diaphragm with soap and water and wiped out the chamber and tube with a carb cleaner soaked rag.
Since I didn't see anything wrong up top, I pulled the bowl again and pulled the main jet, tube, and the little piece that sits on top of the tube and goes into the hole to the throat. There are plenty of warning out here to make sure that piece is running in the correct direction, so I just wanted to make sure. Of course, the second I popped it out, I lost track of it's orientation. I cleaned up some varnish off that small part and the needle. I also took the time to check the float level this time - it was out, and then I patiently reassembled everything back together.
With everything back in place, she started up on the first attempt, and even idled reasonable well out of the box. Off for a test drive. The slow return to idle was gone, so problem resolved. After letting the bike warm up, we hit some larger roads that let me check the mid and top end circuits and all seems well with those areas. Plenty of acceleration through the mid and high ends, and easily went to 60mph as it always has. No popping when downshifting or going down a hill in gear.
So, another happy ending! Thanks to anyone and everyone for posting all the fantastic technical advice, opinion, photos and folklore that help make this one of the most useful site on the internet - for TW owners anyway. Peace!