The Rotella 15w-40 had actually sheared down to about 12.5 cst @ 100° (with a small amount of fuel dilution per Blackstone’s calculations). But no, I don’t credit the oil change with the entire 2mpg, it just makes me feel better about paying twice as much for oil. Factors like a new air filter, new fuel filter and a fuel delivery on the same day might have played a role (I use bulk fuel, this delivery switched me from 10% #1 to straight #2 with summer fuel additives… that being said, this was a year ago and my mileage didn’t drop significantly this past winter).
The truck had 30k on it at the oil change, might have been the sweet spot for breaking in, maybe the Schaeffer’s isn’t doing anything other than making me think the engine finally sounds healthy.
On the other hand, maybe the engine was dying for those friction modifiers Schaeffer’s is so proud of, and maybe the T6 formulation just didn’t mesh with my rings.
That’s the problem with a lot of these anecdotes, even with UOAs there are too many other factors. But anecdotes and more compelling evidence from others really suggests that Schaeffer’s is a good option on these engines, especially if you plan to keep it for a few hundred thousand miles like I do.