the service truck at my work, a 2011 chevy 3500 flatbed with 3 toolboxes and air compresser gets like 11

Yeah deleted I can see that.

My duramax saw 20-21 all day on the interstate.

The Urea fluid wasn't introduced on production diesel trucks till 2011, before that the trucks just used diesel out of the tanks to inject into the filter to burn off soot.

When your truck goes into regen it is required to run down the highway above 60MPH for a period of 15min to 20min depending on truck. sometimes depending on how hard you work the truck as in pulling something all the time are carrying loads will determine how long it'll regen. If your truck goes in to regen and you do not finish the regen you will have the potetial of shutting the rig down and the truck does this to save the turbo and truck internals. The exhaust temps will go into excedence of 1200 degree exhaust temperatures while this is going on.

All the trucks use a slight amount of diesel to help with burning of the soot in the DPF filter, thats why if you pay attention to the MPG setting when your truck goes into regen you will notice a drastic decrease in MPG then it'll go back up when the truck has finished a full cycle of regening.

I've heard there is nothing you can do with 2013 models, is this true?

Should still be able to use sims

1200 degrees LOL my record high on my edge monitor says 1641 as my all time high

yes i know this isnt good, but i won the 1/4 mile that pass. and no i dont run my truck hard very much at all. in the summer i can set my alarm off at 1320 pulling a mountain on the way to work but thats usually just in the summer, and thats romping it up the mountain.