I'm in a similar boat as you right now. I wasn't throwing a code, but now after replacing all 8 injectors I still have the problem and a P300, P302 and P305 code now. All of my plugs are good too. Let me know if you figure yours out and I'll do the same if I figure mine out. My voltmeter on my dash is also fluctuating but when checked at the alternator and the battery my voltage isn't fluctuating.
2003 Jeep Grand Cherokee Overland 3" IRO springs (actually got 4" from them) 4.7L HO, 1 1/2" wheel spacers, Magnaflow exhaust
TEOTWAWKI: The End of the World as we Know It (Acronym coined by Mike Medintz) (Spoken “Tee-ought-walk-ee”).