why didn't Jeep (or Mercedes) tune it like you do from the beginning?
2007 was the phase in of the "Tier 2" emissions standards to light-duty passenger cars, including your Grand Cherokee CRD. What this means is DaimlerChrysler (at the time) had to prove to the EPA that the emissions emitted from the tailpipe did not exceed specific limits set forth in the "Bin" category of the vehicle for both the 50,000mile point as well as "end of life". The tailpipe emission most closely watch in the diesel world is the NOx, which is a direct result of the combustion temperatures. Rich combustion = lower NOx, but worse fuel economy. Conversely, lean combustion (ie more air for every one part of fuel) will give better fuel economy at the expense of higher NOx.
Jeep didn't do it this way from the factory because they weren't allowed to. Are you going to notice the higher NOx with an aftermarket calibration? - Absolutely not. I don't have emissions data for the GDE calibration, but I'm guessing it takes it back to 2003-type levels, which is still clean in my opinion. Write your congressman and ask him to push an agenda of fuel economy vs. emissions regulations. This has historically been the direction of the European "Euro" regs (which is why their cars get 40+ mpg)
Also, I was looking into a DPF delete and using a tune from another company, but do you think a DPF delete would make much of a difference with this engine? Thanks!
The back pressure of the Jeep DPF is very low, with regeneration events only occurring every ≈750 miles. There's not a lot of fuel economy to gain here. In comparison, DPF regenerations on the Big 3 diesel trucks are more like every 60-200 miles, so there are bigger gains with delete kits on those vehicles.
My suggestion... go with the GDE calibration only, and enjoy the mileage gains and extra skinny pedal it gives you.