Oil Catch Can from Ebay Installed

Similarly, my observation is that my Gen2's oil consumption primarily arises now when driving above 75mph.

I would suggest that you do the following: i.) install an oil catch can; ii.) start "short sticking" the oil at each oil change (using only 3.5 quarts at oil change with filter, rather than Toyota maximum of 3.9 quarts); and iii.) start using high detergent/anti-sludge oil at every oil change (my favorite is Shell Rotella). And, then observe changes in oil consumption and report back your findings here.

My CEL (DTC P0420) came on for the first time* last week since installing the oil catch can (about 10 months ago). I reset the code with the Torque app and this DTC has not reappeared after more than 500 miles of driving (since the code occurred). I have no other DTC codes appearing.

*- another instance of CEL (DTC P0420) occurred after installing the oil catch can but was attributed to my failure to timely empty the oil catch can.

PS Gummed up oil rings are likely the cause of oil consumption in your Gen2. My experience was that after about 12000 miles of driving with the high detergent/anti-sludge Shell Rotella straight 40W, the Gen2's oil consumption started to reduce significantly (my interpretation is that the gummed up oil rings had "un-gummed" due to the Shell Rotella detergent and anti-sludge compounds).

Compression test results should be retained. So that you can compare results in the future (and determine whether the problem has gotten better or worse).