If you post public links to the test sessions in Training Peaks, then I can take a closer look. (If the terrain was flat in the drift test, then Pa:HR is the metric to go by.)
To your questions:
1.) Should I use 165 as my AeT, bump it up a bit (maybe 167?) given the Pa:Hr of 0.76% , or retest?
This is false precision. Heart rates aren’t that accurate. Once you’re within a 5-beat bucket for a threshold—or a 10-beat range for a zone—that’s as close as you’re going to get. Also, once the HR range of Zone 3 is narrow, changes will stop. At that point, the most important training begins, focusing on improving pace at those same heart rates.
2.) Does my AnT test Pa:Hr variation of 1.86% imply that I tested poorly (should have gritted it out longer) and should retest, or is it fine?
No, it’s fine. Drift doesn’t have much relevance to an AnT test.
3.) Using the current AeT/AnT, it shows I need more high-intensity training.
No, it shows that you can tolerate more high-intensity training. “Needs” are determined by goal events, not heart rates.
I’ve read the article talking about when and how to add in high-intensity training, which is very helpful. I’m in Week 7 of the 24-week training plan, preparing for a mountaineering course in Alaska in late spring. I don’t want to ruin the integrity of the plan. So my question is how should I modify the training plan to add the high-intensity work (e.g. replace a day, tack it on after another workout, modify say my run/hikes to add in intervals)
I would just stick with the plan. High-intensity is less important for all-day events like mountaineering (compared to a 4-minute skimo sprint). The plan as-is will prepare you well.
4.) Finally, as you can see from my TrainingPeaks pictures, I’m a turtle. My AeT pace was 10:38 min/mi. I want to make sure my pace isn’t the weakest link for my rope team when I’m in Alaska. Should the 24-week plan also improve my speed as my fitness improves?
If your thresholds are as close as you think, they likely won’t change much at all going forward. This (pace) is where you get to focus now. Heart rates while training will tell you if you’re at the right intensity, but future threshold tests should focus on pace to measure progress.
Related to that, changes in threshold heart rates are relatively quick (many months) while improvements in pace can continue for a decade. With an event-specific mix of base and intensity, your speed will increase.