2015 RT 5.7 M6
I thought it was the block but the OP has a 6.4 so it would be orange in color (I assume since car in image has SRT badge on the grille). Looking at it again I am guessing the black painted surface is an aftermarket intake like edelbrock or maybe supercharger head...that and the way the oil pools makes it look like the rockers were correctly installed.good spotting that - that looks like the lower side of head by the block (black paint on 5.7 blocks) and if that rocker shaft was installed like that, its not correct.
The pushrods are different lengths for intake vs. exhaust and I'm not certain about the rockers, I'm aware they're 1.6:1 ratio.
you have a 6.800" set and 8.100" set of pushrods for the intake / exhaust positions
the intake rockers are clearly marked with the "I" cast into it. it might be a positioning thing or the arms or the geometry is different. I just know to reinstall them in their correct orientation on the engine
Not sure if it is physically possible to install the pushrods and rockers in reverse (i.e. intake to exhaust and exhaust to intake)? If it was I am sure it would have ran like crap to begin with and OP said it was running for a month, if I read that right.
If the spring kit came with retainers for a 5.7 and 6.4 it could be that the wrong one was installed.