I'm beginning to think there is a problem with the computer in the freightliners, either when AE programs or has them built to their wants or when something, most freightliners I've driven here at averitt the fan automatically starts up when taking off from a stop or slow roll, even before the temp has a chance to raise. Averitt has gotten the transmissions shifting different, because they were having a problem with the Y-split/shifter or something, there is only so much you can do before the unit starts goofing up, those motors are built to run one way and the next thing you know they have been programmed to run/shift another. I've read the fan will rob you of 15% of fuel mileage and horsepower.
I worked for an owner/op many years ago, he had the belief if you had the motor unrestricted with a smart driver who wouldnt abuse it that it would get better fuel mileage. He bought a used truck that was cut back, drove it for a week, took it back and had the restriction taken off, mpg improved .4 mpg. One could argue it was the difference in driver, (but it was his truck and had no reason to play with the numbers), but otherwise it was on a dedicated run hauling less than 5k loaded, and in the summer with no rain/weather issues during those 2 weeks.