Join Date: Aug 2017
Location: Morgan Hill, CA.
Model: GL1500 Interstate (Cinnamon/beige)
Others have more knowledge/experience than I have, , , but if you're gonna continue running a Shinco rear, I think you'll be pleased with the results of max pressure (from mfgr) and balance beads.
The new suspension could be contributing to the cupping, , but the tire pressure and balance beads will be the most effective solution to cupping. The bike could "handle" better with a stiffer suspension if that's an issue for you, , , wouldn't hurt to give it a try.