I'm going to try and describe what I'm feeling when I shift up or down on the bike. To me, it feels like the rear wheel and chain is torque shifting side to side, ever so slightly, but I can feel it. It's done that since I got it, I kind of felt it was inherent to a vintage bike and not having ridden a chain gear bike in 25 years or so. So, when I go from first to second and roll on, the back end feels like its a torque movement as long as I roll on. When just cruising, it's not there, but if I down shift, it does it as well. New wheels, new tires, but running gear is old. I've checked the axle nut and no slip there and when on the center stand, no excessive runout. What gives?