Normally the OEM tag is sufficient to carry the load of a van at rated weight. I have never seen one that is for an empty van. That said, tire pressures at the minimum for capacity usually don't handle all that great, as the pressures are too low for best control. The Chevy tags give 50/80 on them but most will run 65/80 for better handling.
If you have a 2500 van with load range E tires, you will have quite a bit of window to work with, so don't be afraid to move the pressures around until you get the feel YOU like.
"Normal" rules would say that if the van feels twitchy as in steering too quickly for your taste, you would reduce front tire pressure and increase rear tire pressure. If you feel like it is sluggish and gets pushed around in the wind a lot, increase the front pressure, and maybe reduce the rear if needed.
Your tire pressures are going to vary by at something like 5 psi over a days drive, so keep that in mind, especially if you feel it getting worse or better over a day. That way you can compensate.