Just an update for my P2138 issue. Turns out the problem lies in a aftermarket cruise control I had installed right after purchasing the vehicle. The cruise control likely damaged the accelerator position sensor in the pedal assembly (even though it took 6 years to do so) After replacing the pedal and removing the cruise control, everything works like a charm. Will update with anything else that's relevant.
I need to write myself a note to remind me to never, ever, ever get aftermarket electronic modifications done on my primary mode of transportation. Keep the major electronic mods for my weekend fun car...