owner operators please respond

yup my t600, with a 3406e, 13 spd and 3.55 rears does pretty durn well....i havent recieved my quarterly ifta report yet, but when i do im sure it will say im averaging right around 7.2 mpg ( my math may be wrong but hey...i outta be close), but keep in mind alot of my flatbed loads are low and heavy, and i never run over 68mph....not even to pass unless its downhill....lol

 

Well I guess my current truck has left a bad taste in my mouth or cats. It's just horrible and we can't figure out why other than the rear ends are too low. It's a c15 set to 475hp and it oes 5mg on a good day. I just got back from California the other day. IT was a RUSH load so I ran 75+ all the way out and I was down below 4mpg going out (I bobtailed back)
I drive this truck 55mph in IL with an empty van trailer and I can only get it to like 6mpg. Oh an most my load are like 18k pounds but the one this week was an MRI scanner so I was right at 80k

Oh, and did I mention the truck pulls like dog sh$@!!! I got passed going uphill by a schneider truck last week. talk about embarrasing

 

I think it's time to put it on the dyno and see what is wrong. I would check the aftercooler for air leaks, all turbo pipes, air filter, and the engine temp sensor that sends the temp to the engine control module.

If that sensor is bad it could be telling the computer that the engine is cold, and richen up the fuel and change the timing.

It could be time for a valve adjustment by someone who knows what they are doing.

Don't forget simple things like a draging brake or low air pressure in the tires.

If your torque is set high, say 1550 to 1850 ft.lb., then you should pull good.

 

the torque is set to like 1600. It was just in the shop to be looked at and they didn't find anything.
One thing I am noticing though is that the air conditioning is getting funny. it will blow warm and I have to reach down and turn the fan on manually then it goes cold again. I'm not familiar with the new motors so I don't know if there could be a relation to the sensor that kicks in the fan for the ac and the engine temp sensor. You may have something there.