Isx detuned?

[Lonestar10]

i know when i worked for crete when we moved from 62 to 65mph they didnt just change the speed limiter they had to put a whole new fuel table in the trucks so its possible it has an adulterated fuel table. your dealer should have installed an owner/op tune in it before he sold it to you.. i would go to said stealership and ask them to make sure the tune is an actual cummins tune not something some desk jockey thought was a good idea.