There is no rime or reason to what my 2009 does it will sometimes go past 5000 miles and sometimes not make it to the 2000 mile mark under the exact same conditions.
I work for a utility company with a large fleet of vehicals and all light duty trucks go 5000 miles on an oil change and the fleet managers dont care what the computer says. These trucks Idle all the time, running a pto or just charging batteries for inverter power. The old trucks did fine and the new ones ,had better do the same.
I idle my 2009 with AC on for extended times and I have had to have the system cleaned 1 time. But what the heck I bought it to use and it better be able to do that, and take care of its self or it wasn't worth the 50k I paid for it. The last 2 trucks I had worked fine.