360 runs great one day and then poorly the next

more detail on "runs like crap"
Idle, cruise, WOT no load, WOT under load, does it every go from running well to abruptly running poorly, or does it only run poorly once it's started that way?

I would start by closely checking all your plug wires, to include resistance, then checking all your wiring.
make a list of your checks, then do the same checks with the engine fully heated up.
And a part being new pretty much means nothing. Every part works correctly, right up until the point it no longer does.