2014 Volvo 780 Ishift - Bad Fuel Mileage

Last month I rented 2 2015 780's, both with approx. 350K miles on them. One was governed at 75mph, and the other at 80mph. Both trucks had the D13 w/I-shift.
After crossing into AZ, I had both trucks maxed out at speed for 126 miles, grossing approx. 55K GVW. Both trucks averaged over 7.8 mpg on the computer.
My average for the 850 mile trip was low 7's.

 

Ok, but shouldn't you feel that the clutch is slipping?
At the Volvo the computer usually notices and gives you a warning.
My fuel mileage differs often between 5 and 8 mpg and I always ask me why?
The wind is a huge factor.

 

No clutch in the transmission. Clutch is before the transmission on the end of the crank and if it was slipping he would be getting codes on the dash.
1st problem is hauling a container. Always get less mpgs hauling a can. How fast do you drive? How was the weather and wind? too many variables. A 30 day average is always the best way to judge your fuel mileage.

 

If you get clutch protection code what are you doing to get it? And you should stop that. If you have clutch issues and they look up all the protection codes they may deny you warranty.

 

If you idle truck often,fuel average going down extremely fast

 

Getting good fuel mileage also depends on if your I-shift is a direct drive or has overdrive, and what your rear end gear ratio is.