How do you know that the FM that could be resulting in the change isn’t the same between the two oils? Whatever is causing it may be more present in the SuperCar blend, but if there is sufficient in the Premium Plus to still get similar or almost-similar results. The only real way to tell would be for Skippy to try the SC at some point and see if the rumble is further reduced.So if your MDS is “noticeably smoother” using the premium plus 0w20, that tells me that the supercar 0w40 additive pack in OVERKILL’s special blend is not the variable that is smoothing out the “MDS rumble”.
With that said, yours is “noticeably smoother” while he described his as “imperceptible”. It’s possible that the difference between smoother and imperceptible is the difference between his Grand Cherokee with its 6.4 vs our Rams with the 5.7l. As for his Ram, it could be the difference between our older body style without dampers vs his with the dampers.
I need a cup of coffee. My brain is working too hard on a Saturday morning.