Appreciate the many contributions, much of which have outlined my very thoughts.
Some Q’s from above answered:
2012 3.5 exoboost, the first gen of engine, an absolute hoss to pull with BUT DI only prone to intake deposits (now walnut blasted clean), long/vulnerable timing chain (replaced at 101k mi). Bought from friend, kinda bought a lemon ? - sludged near death, but rolled the dice and had it scraped/cleaned 80k mi ago, HPL last 50k mi, and runs strong, powerful, and quiet. In shop this moment for a complete exhaust side replace/upgrade - small turbo size bump, high-flow downpipes & exhaust.
Uses no oil i can tell. Gets lousy 13-14mpg. Don’t plan to tow much/none this winter, expecting to put another 10k mi on before warms up. Yes, MT. Like rlsewhere at this latitude, nothing to be -20F, sometimes -40F over winter for week or two, and places i need to go.
Truck specs 5w30, but “they” have found better timing chain life on Xw40, so i stick with that. HPL 0w40 PremPlus is no doubt both cleaning generally, and terrific performer/spec. Does it clean rings? No factual proof exists. Not a onock, may just not be in the cards. I question if VRP 5w30 may well scrub these ring packs out in a season of use, and i can go on believing (hoping) this engine is as cleaned up as reasonably possible and work the snot out of it another 100k+ mi. It’s just, 5w30 is a small step backward. But for 10k mi of light-work winter use? Think i’ll go for it. Am not going to be towing heavy this season, nor even dropping the hammer on snow, so.