Ok, as a preface, I've just learned of the crankshaft sensor mod and the potential difference this can make in terms of timing advance. I know the crank sensor was replaced prior to my acquisition of the vehicle, and I'm thinking it might be bolted in place in the direction of being more advanced. Without even making an attempt to get under the car and look, I'm just going to fill up with premium on my next tank and take a look at the numbers once I'm solidly into the tank of premium.
As the issue currently stands, however, the engine runs really well 90% of the time, as it only exhibits this behavior when under load, low RPM, at speed, most severely when in 6th gear. It has set zero codes, and none are pending. The misfire count is also zero from what I can tell. This seems to be pure and simple KR, something I'm familiar with, having owned a force inducted vehicle, but wasn't expecting on a 10:1 N/A V6.
During these events of timing pull, which is as much as 4 degrees negative timing advance, the engine stumbles noticeably, as you might expect, and power is non-existent unless you depress the accelerator enough for a downshift, in which case it is found that up to 40 degrees of timing advance appears to be available in every other condition, and the engine seems moderately powerful and smooth. I'd like to see some higher peak timing advance, but I've no idea what the PCM's parameters are set to from the factory.
The engine is completely up to date on maintenance. OEM plugs, PCV, new intake gaskets (during plugs), and long term fuel trims are within 3% of 0%, with less than 2% variance between banks.
Here's a long video of different driving conditions to show exactly what the behavior is with some fundamental parameters displayed. https://youtu.be/IZzoMnvIAMM