I have a Seismic 355W and I picked it up from storage today. I was underneath just checking stuff and notice cupping on the edge of my tires. Both sides. Left front is the worst, with significant cupp...
Steel wheel? Have it balanced with a lug centric adapter on the machine. Hole in a steel wheel is just stamped and not always centered perfect. The standard cone adapter will have the wheel off center. Some worse than others.
Also you could have someone follow you to observe the tire if it is really bouncing badly.