Your decrease in fuel economy could be from winter blend diesel. It happen to me when I installed the. DPF delete last November. Was disappointed a bit at first, but looked back over the last few years on my fuel usage spreadsheet (been keeping hand calculated since new) and there was an improvement. Lot better in the summer.
2008 CRD QDII, OME HD, Pintlers wheels with 265/70/17 Goodyear Silent Armour's, Jeepinbyal UCA's. 4XGuard Front guard, Side Guard, belly guard, Matrix HC. GDE ECO Tune w/ delete.