Im am as mopar as one can be but I can admit that the 5.7 in these trucks is weak. I had a 73 charger in HS that came with a 318, swapped that for a RHS 360 (RHS was a subsidiary of comp cams that built high performance engines in the 90's) then a 440 and from there it was a 89 Shelby Daytona. I love mopar but the 5.7 hemi in trucks is a dog, its a vast improvement over the 5.2 and 5.9 but that's it. I bought a 2003 for the new body style but mainly the HEMI. That said, the HEMI's intake ports are simply too large for a street engine in a heavy truck, this is why the engine feels lazy. Dodge tried using VVT and an adaptive intake to help with this and it did but the ports are still too large.
Large cfm intake ports make great power up top but they suck down low as there's no port velocity and port velocity is what promotes cylinder fill which is what makes low speed torque. Dodge needed a different head for the heavy trucks, the Eagle head is 215 CC and flows 330 cfm at .600 valve lift. That's a decently flowing head on a performance application but too much for 345" in a heavy truck and the way this trucks drives show that. For comparison, my LS heads flow ~400 cfm with a 285 cc port and that port is really too big for my engine that's 450".
No way a 5.7 needs that much port NA but throw boost at the HEMI heads and they absolutely scream which is why the hellcat engines run so well. I don't believe the SRT 6.4 would make these trucks any better as the 6.4s TQ curve is even further up in the RPM range which is fine for the cars but you don't want that in a truck.
The only way to make the 5.7 "better" is with boost; you'd only need about 5 lbs. For me, just looking at either of the hurricane twins dyno curves, both are superior to the HEMI.
I don't buy the longevity claims either as the engine is overbuilt but also, reading here, many people aren't keeping these trucks long enough for any "long term" problems to be an issue.
My next truck will likely be a tungsten with the HO and as mopar as I am (I'd love to build a 68-70 Charger with Hellcat variant), I won't miss the 5.7 HEMI in these trucks