Two thoughts on Diesel and Theo post. Over the last year I have gone to "oil school" regarding the new synthetics and rapidly changing oil formula's. I have concluded that RL, PUP and Amsoil are what I call Tier 1 quality oils. But that does not mean that anyone of them will have the same effect or results in our Hemi engines. RL has proven, for many members to be an effective Hemi engine oil. After experimenting with several oils my 03 5.7 with 230k miles found RL 10-40 to be the oil of choice. Quite and smooth. But there is a learning curve. RL is a high detergent. When first used in a HM engine you can experience internal engine noise in the first 500-1000 miles. After the molly additives take their set, it gets quite. Now that said, RL 10-40 is not sold as a HM formula. I have found that most people who have experienced positive results with RL, used in engines with less than 100k miles. I also use RL 5-30 in my 87 Turbo Grand National. Best oil results I have ever had in that car. In my 2018 2500 6.4 I run PUP 0-40 for warranty reasons. I too believe that blending viscosity when using PUP can make sense and provide increased dry start and wear protection. I found that PUP has a bit lower density than RL. If RL had a MS12663 certification I would use 5-30. This truck is being replaced by FCA. When I get the replacement truck I have decided to use 4 qrts of PUP 5-40 and 4 qrts PUP 0-40.
