Fuel economy suffering, don't know why.
I have an 06 ISX 15 450HP. Over the last two months Ive noticed my mpg go down when I thought it would go up. First summer with this truck and new o/o. Just had an overhead last wk and one injector was replaced. Tests for egr, injectors good, no loss in power, fuel rail pressure good relaced both fuel filters. Im losing about .5mpg to .75mpg. I do have an apu and use approx 4-6hr a day (didnt think the apu would use enough fuel to have such an mpg drop). The only thing I can notice different is it feels like I need more pedal pressure to get up to speed even with light loads. None of my brakes are sticking. Im lost and two mechanics Ive talked to are lost. Any ideas?
Is this a worthwhile discussion?