Well, after a few days of driving, I can pretty safely say that a faulty replacement TPS was to blame for the idle problem. Haven't had any idle issues since I swapped the old one back on.
I do, however have a new little problem. It seems now that while cruising on the highway, if I hit a bump in the road, the engine briefly surges up about 200 RPM before returning to where it was. So, if I'm cruising 2,000 RPM and hit hit a bump, the RPM will jump to 2,200 RPM and then settle back to 2,000. Possible fault in my old TPS? I will say that the old TPS seems a little loose and if you tap on it, you can actually hear and feel something vibrating. Genuine OEM TPS is gonna set me back a hundred bucks though. Kind of a lot to spend on a guess but then, I'm pretty sure the TPS shouldn't "jingle" when you tap on it, LOL.