Well, after several days of testing, tinkering and reading, I was finally able to nail the problem down.

It was the HS-50 servo. I don't know why, but no matter what I tried, I couldn't get rid of that wag, so I said screw it and pulled the servo off. I replaced it with a very standard, slightly slower Futaba servo......one that came with my 6EXHP radio setup. I set my gain back to 60%, set the delay to almost 75% and took the Rex out to give it a try. Imagine that......it cured the problem.

My tail was rock steady, but still responsive. Perfect.

Why on earth would I need to use a slower servo to acheive the results I was looking for?!?! Everyone seems to like the HS-50s, but considering that my other Rex has the same problem, and it also has an HS-50, I'm not sure about them anymore.