From one 6.0 owner to another have in your mind that any device that can idle the engine when parked (Running the A/C, charging controllers, or anti freeze controllers) can cause major problems specific to the 6.0. Vans that have these type of controllers will be more likely to have idled more. I don't mean to scare you but on a van that has one of these I would look at the list of 6.0L improvement mods that have been done and maybe pull the EGR valve (not a small job but no big deal if you've done one before) to get an idea of what soot is in there and if it's been idled a lot. One way folks limit the issues with idling a 6.0 is a High Idle switch which raises the rpm up and limits coking of the intake and turbo. Could one of the dash switches be a high idle switch? To test you will need to set parking brake, foot off the brake peddle, obviously be in park with motor running and flip each switch give it a minute for idle rpm to increase.
Just some thoughts.
2005 SMB RB 4x4 6.0 PSD
A rocket on the pad is safe,
but it's not what rockets are built for.