I have a 03 Chevy Express 3500 with a 15ft Supreme Corp. Box mounted on the chassis. When the chassis was new, it was rated at 12300 GVWR, after Supreme mounted the box, they re-rated it at 12000 GVWR. The truck scales at 8350'ish. So that puts me at about 3500# payload, but I try to stay under 3200#, just in case someone weighed something wrong... and I log if I go more then 100 miles from the office.
Mike Linthicum