General International 15-250 Sander

Anyone have one of these? I have a new one, and am having a terrible time getting it to work right. Keeps throwing the sanding rolls off the drum. I replaced the retention clips - better, but still a problem.
Looking at other posts, and talking to GI, it seems the issue is "trying to take off off too much material". Yes, and I know this is a sander not a planer. But I'd appreciate suggestions on adjustment and operator technique. This thing is so damn sensitive that an eighth of a turn of the handwheel can be the difference between no sanding and throwing the sanding roll!
Also, the GI sanding rolls for the machine are 4" wide, and damn expensive, while most of the aftermarket rolls seem to be 3" wide. Is it possible to use 3" wide sandpaper rolls with this machine?
Lastly, I want to use this machine for finish sanding. What grits on the two drums do people use?
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