I used to have a similar issue when I'd bolt a luggage rack on the back of mine and throw a few items on the rack. I had a relatively new Works shock at the time, tried all kinds of different preload settings, and it never made much difference in removing the weaving. I came from a sportbike to the ST so I had my forks preloaded a bit more than stock, and heavier oil, so the front wasn't as plush as a stock ST. My front ride height was a bit higher than you'd have with the stock fork setup, and my shock was tuned to 'sport' stiffness. I'm also about 175lbs FWIW. It seemed like many STs had that issue, and others did not, but the cause of the weaving was never revealed to me. Since I don't ride with the rack very often anyway I stopped thinking about it years ago.