Update:
Finally had a chance to recreate the conditions previously mentioned, and while the noise seems to have lessened some, it is still there along with what I feel is a lack of power, coupled with a "burning" smell that's noticeable under heavy load after about a minute or so.
I'm starting to question whether the cheap Amazon catalytic converter I installed is clogged or failing and causing both a lack of power and valve flutter at high RPM's that are causing both the noise and lack of power up steep grades. I haven't checked back pressure yet but I do have a gauge to do so if that would be prudent.