I subscribe to a few automotive service trade magazines and they have some good information that you might find valuable. Here's a recent one concerning 2008/2009 6.1 Liter Grand Cherokees:
Rough Idle, MIL Illuminated, DTC set.
Some '08 & '09 Grand Cherokees with the 6.1L engine may produce a rough idle on cold start-up with the MIL illuminated and DTC P050D stored in computer memory. If routine diagnoses fails to reveal the cause of these symptoms, a glitch in the PCM is likely the villain. Reprogramming the module with an updated calibration is the only reliable fix, says Jeep. To do the flash, you'll need a StarSCAN scanner with the latest software version. The calibration files can be retrieved off the Internet. After the programming job is complete, fill out an Authorized Modification Label and attach it near the VECI label.