You can try varying your oil grades based on the season. Try the 5-20 if you have cold winters. And the 10-30 in the summer. In more extreme climates like where I live near Phoenix, or up north with colder winters, I can see a use for a slightly different viscosity. However the change the dealer mentions is so small, I would think the benefits are rather small as well. I'm not accounting for the design flaws you spoke of when I make these assumptions. They're just generalties that can apply to most cars. Did you try switching back and did you have similar issues again in the first 2 weeks on the other grade? In different seasons? The grades have more to do w/ viscosity variations. (you know, higher number, thicker oil, etc) Auto makers are also using thinner oil to increase the fuel efficiency to meet the EPA requirements (or whatever agency regulates the avg MPG for a fleet). If you live in a temperate climate like the coastal areas around Los Angeles or San Diego, you could even use plain old 30 weight. Not many people would do that, but you can, and I did in my older cars for quite some time when I lived there. That's just an example btw.
As for the knocking, well keep in mind the possibility that those issues may not have been fixed as well as you are led to believe. It is a dodge after all. They could be fixed as you said, but keep that in the back of your mind while you try other possibilities. Sounds like it's time for some shade tree troubleshooting. Take a long screwdriver, or metal rod (not close to the fan or the belts though) and use it like a stethoscope to try to pinpoint the source. Touching one end to your earlobe, and the other on different parts of the engine block.
Also listen to see if there is any constant rhythm to the knocking sound. If so, maybe an accessory, or the even belt itself. Then there's also the much loved warranty method of getting it repaired
It should still be covered under a drivetrain warranty at the vary least. Should being the operative word here. Also swing by the dealer right after the oil is changed and have them listen to it.