A while back I had a Grand Cherokee with a 4.7 liter that did pretty much the same thing. It kept giving me a random misfire code and the injector open / short circuit codes. I would clear the light and after about 15 minutes it would come back on but there was no rhyme or reason to it. Sometimes the injector codes would be on some cylinders and then I cleared it and it would be on different ones when it came back on, it didn't make sense. After clearing the engine light it would run great for about 15 minutes until I came back on and then it would start to misfire. Eventually it got bad enough that it would almost stall in traffic. It ended up being a bad MAP sensor even though it never gave me a code for that. Someone in one of the Grand Cherokee forums suggested the map sensor and that's what fixed it. I got it out of the junkyard out of a 4.7 Dodge Ram. You might want to try that before replacing the expensive PCM. I don't know anything about the front control modules or any of the control modules you're talking about because the Grand Cherokees don't have them. What I do know (and it could be different because yours is newer) is that limp mode only occurs for transmission problems as far as I know. I've never heard of limp mode for engine issues. If you want I can give you the link to the factory service manual for the WK Grand Cherokee which is what I use for my mother's 2006 Commander. It's pretty much all the same wiring.