Wanna help me out with the lingo???
No problem.
The jist of it is to check for issues regarding airflow, fueling, and/or injection pressure. As any of these aspects, when not working correctly, can cause huge drops in fuel economy regardless of the tuning. Then add to it the winter fuel aspect, which also attributes to a drop in fuel economy.
Winter fuel is a blend of #1 and #2 diesel. #1 doesn't burn as well as has a lower BTU count than straight #2. So when that's blended in, a drop in fuel economy is almost always seen. It's very common to see a 1-2 mpg decrease, especially in a lifted truck. The blending however is necessary to lower the cloud point of diesel fuel and help prevent gelling in the winter.
Boost and exhaust leaks are common, with some being easier to diagnose than others. Exhaust leaks will be accompanied with visible soot marks on the back of the turbo where the collector bolts in, or at the up-pipes leading up to the back of the turbo - particularly where the pipes meet the collector. If you spot soot in any of those locations, you have an exhaust leak. Exhaust leaks reduce drive pressure, and thus reduce boost. This causes higher EGT's (exhaust temps), and lowers fuel economy.
Boost leaks are harder to spot since there is typically not a tell-tale sign like soot. For those you would have to visibly inspect the boots or even pressure test the CAC (cold air charge) system for leaks. To pressure test, you have to build an adapter that fits into the inlet of the turbo.
IPR/ICP refers to the high pressure injection system. These trucks build injection pressure through the usage of the high oil pressure pump, located directly beneath the fuel filter. IPR stands for Injection Pressure Regulator, and is located at the back driver's side of the pump. It regulates the oil pressure to the injectors based on what the demand is calling for in order to help deliver a specific quantity of fuel. This can be anywhere from 500-3000 psi, depending on load, pedal position, RPM's, and the tuning itself. ICP stands for Injection Control Pressure, and the sensor that monitors and actually sees that pressure is located towards the front of the driver's side oil rail on top of the head. This sensor reports back the actual oil pressure to the PCM, and that information can be used by the PCM to adjust the IPR duty cycle to either increase, decrease, or maintain that pressure. If any of these two systems are malfunctioning, you can have issues with how the truck runs and idles, as well as fuel economy issues. However, if the truck runs and idles just fine, these typically aren't the culprit.
The EBPS is the Exhaust BackPressure Sensor, and is located at the front of the engine. A tube underneath that sensor runs to the passenger's side exhaust manifold. This monitors exhaust backpressure and is used by the EBPV (Exhaust Backpressure Valve) in cold situations to block of the exhaust pipe and create a load on the engine to speed the warm-up process. If this sensor malfunctions or if the tube is blocked with soot, the valve can end up staying closed at times you are trying to accelerate or maintain speed. This will cause a hit on fuel economy. However, the very noticeable signs of this are an extremely sluggish engine when cold while you are trying to accelerate, and the truck will barely get out of its own way.
The CPS is the Cam Position Sensor, but it's something that you probably don't have to worry about. If that fails or malfunctions, the truck won't even run to begin with.
First order of business would be for you to check for boost and exhaust leaks, as these are far more common issues that would cause a loss in fuel economy. Other than that, you also have to consider the configuration of the truck with the lift and tires as part of the problem.