Had my 90 on the bump-stops a few months ago when I was picking up ballast and yes, they do handle a little strange like that! Been very close many times but only actually done it once.
It is fitted with HD springs but I got so used to loading it up that I went over my usual amount by a considerable quantity and it was only when I noticed that I wasn't having to lift the stuff so high to get it into the back that I took a peak underneath. Sure enough it was on the stops (usually I leave myself an inch or so of travel!) so I removed a little weight but then drove it home more concerned about over-loading the axle than anything else.