Do you think that Mobil 1 FS 0W-40 is really the best oil for the 3rd Gen HEMIs?
Sorry for the late response, missed this one somehow.
If you have a RAM 1500 DS then running your engine cooler is the best thing you can do. Mobil 1 FS 0W-40 is the best off-the-shelf motor oil you can buy, yes, it is by leaps and bounds better than PUP 0W-40.
What you also have to understand is that boutique oil blenders like Red Line start out with pre-made cookie-cutter additive packages that they purchase from additive manufacturers like Lubrizol. They get to choose the base oils, and then they get the recipe how to tweak and enhance certain aspects of the additive package. That's why you see 600+ ppm Moly instead of 80ppm, because Roy Howel at Red Line is convinced that Moly is a superior friction modifier to organic friction reducers, as in "it lasts longer."
When you leave the world of API licensed oils, with a few exception like Royal Purple, you can buy a superior oil like Red Line, HPL, Driven, Motul, and others. No, I'm not mentioning AMSOIL, because they make their motor oils to be in line with API licensed oils. They are meant to last longer, not provide additional performance.
Once again, I'm sorry for the late reply, and I hope this bit of info helps.
Out there in the desert, I would definitively run a 180F thermostat. The best thing you can do for your HEMI!