Following up for everyone, turns out my issue was due to another this piece of plastic still attached to the under-side of my replacement glass. I double-checked for this piece a week ago and didn't find anything, but upon removing the glass from the phone today, I saw it start to peel off. I removed it and after re-attaching the glass, the screen now performs as it did when new.
erebis674, thanks for your response, but what do you mean "you will most likely have replaced the lost adhesive...". I don't see that step anywhere in this guide. The adhesive is removed completely in Step 12 and new adhesive is only placed around the border, not above the digitizer.
Are there any other indications that the digitizer or LCD has been melted besides a less-dark screen when off?
After following this guide, is the phone's screen supposed to appear like it did originally? I ask because people act like it does, but mine (and apparently James') does not. It's much less crisp, less bright, and when the screen is off, it looks less black than originally. Also, the responsiveness to touches is now a bit buggy. My impression is that this is either do to removing the adhesive layer, leaving an air gap between the glass and the digitizer, or me buying a low-quality replacement glass.