I'm running 5w40 full synthetic and I also ran two bottles of rev x, it helped, but still has a cold start misfire,
like I said never messed with any of them and didn't know if it was worth it. from the cost It would be cheaper to put FICM in than two injectors, if I send out my FICM it would be same cost as 1 injector, so that's why I'm just throwing around idea, I have 3 6.0s i own, this is in my 03 2wd excursion has 245k on it, my 05 250 I've ran 5w40 in it for last 3-4 years and it doesn't have any problems, and my 04 4wd excursion I rebuilt the motor and haven't got it running yet.