f450 dpf regeneration/cleaning frequency
 

I have a 2008 f450 with 22,000 miles with which I pull a 20,000 lb.
5th wheel RV. On a recent trip from Florida to Denver (just shy of
the mountains) the "cleaning exhaust filter" message appeared on
the dash display about twice per hour or roughly every 30 miles.
I always use ultra low sulfur df. Though their was never any significant
change in performance, the initiation and duration of the cycle was
noticeable. The issue is more annoying than troublesome. My Ford
service dept. performed the system modifications noted on the
Jamuary technical service bulletin prior to my trip. They are unable
to explain the extreme frequency of this process.
I solicit comments from anyone with information on this issue.
Thanks
jkw