I'd attribute it mainly to winter; warm up times; and I don't know about your particulars of current driving but they're very sensitive to wind on the highway. And the jet stream has been all over the Country as of late
Colder weather affect all vehicles, including gas models. During summer, in city driving, I average between 9-10, during winter I average between 10-11, if real cold spell, can average between 11-12. (km/per 100.)
Once I put on the winter covers, I improved by 1, so now averaging 10-11. Summer time, I don't idle, so idling for 5 to 10 minutes each morning will drive the fuel economy down. The winter covers also improve the REGEN distance a lot, not quite as good as summer time.
I'm a lay back driver, usually do 10 percent over the speed limit, don't do much flooring the diesel peddle.
This can happen often during cold weather. There is where Winter Covers helps. Quicker warmup
Excessive Idle -
Should be avoided when possible and can result in reduced fuel economy and increased engine wear. An automatic shutdown feature is available. Contact a Cummins distributor for details.
Engine Warm-up -
Do not operate at full speed/load until coolant temperature reaches normal operating range. Do not operate above low idle until oil pressure is indicated.
Engine Cooldown -
Prior to shutdown, an engine should be idled 3-5 minutes after extended full throttle or high power operation. However, under normal driving conditions, such as exiting a highway, engine operation is generally lighter in nature and thereby, the 3-5 minute cooldown is not necessary.
A diesel engine idling for an hour uses as much fuel as if the vehicle had been driven 11 km (7 miles), on average. When it comes to maintenance, that same engine idling for an hour causes as much wear as if the vehicle had been driven 40 km (25 miles)
•Improved overall fuel economy and reduced maintenance costs