Is that the model with the injector in the DPF unit? Those have been known to create a high fuel use situation, but not sure off the top of my head what years had them. Other than that, injectors and injection system can do it if the nozzle tips are the least bit worn, poor pattern and overfuelling and it probably doesn't take much to stuff things up there.
Might pay to look at tyre pressures, loading and alignment too, that can cause things to change.
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