Tran service now bad mpg

[Double B]

I have an 06 lbz with 55000 miles at 50000 miles I had the tran service along with oil change and tires rotated. I have always gotten between 18.5 and 19mpg with 285s after you caculate the actual mileage driven. Im a stickler about mileage and know at every quarter tank mark how many miles I should have on this tank. I was on average with the first quarter when I had this done and now I am lucky to get 17.2. The air and fuel filter were both changed at 45000 miles. what did the dealership do to my truck?

[DieselMonk]

prolly winter blend fuel...

[Double B]

Thought about the fuel but mpgs stayed the same last winter as the summer

[Runaway_Dmax]

check tranny to see if over/under fill. Thought I read somewhere that an overfull transmission could cause problems.

[Mark Rinker]

I would bet that the dealership has nothing to do with your mileage variation, based on a transmission service.

Winter blend fuel is the most likely culprit. It does affect mileage. If it didn't before, maybe you were either driving less (sample size), or perhaps less concerned with the fluctuation, before diesel was $3.50 per gallon.

Other ideas to consider:


Proper tire inflation
Dragging brake(s)
Partially plugged cat
Partially plugged injector(s) - do you run fuel treatments?