What is your tire pressure and weight distribution?
Paul advocates 2psi more in the front than the rear. I run about 36/34 on the highway.I've never had tankslapper problems with mine, but if I did I'd try dropping the pressure in the front a couple of pounds, but I'd still keep it +2psi over the rear.
I may not know shit from Shinola
(imagine how the man from Shinola feels about that) but I believe that too many folks put too much weight on the rear. I naturally travel pretty light and don't load the back up much, even for a two-week trip. I carry as much weight forward as I can on a tank vest. A front end that is too light can't stay planted and track correctly.
Once the front end starts to oscillate it will continue to do so, perhaps indefinitely. One way to get out of it is to apply a little rear brake to transfer some weight forward. Gently backing off on the throttle can work, too, because wight is transferred forward as well. Applying the front brake can be bad.
Try, with some help, weighing your bike on a bathroom scale with you sitting on it. Weigh the front tire, then the back. For this exercise it isn't really important to keep the bike truly level. What's important is understanding the weight distribution.
Try this, then we can talk about head bearings.