[Scott Johnston]

Josh:

Here are a few thoughts on your test procedure.  Could it be that the 18% grade made the test muscularly more demanding than your training has prepared you for?  Saying this another way: maybe muscular endurance was causing the high RPE??  With a 2% drift, I’d suggest that your AeT is likely around 155ish.

Was the 20 min steep uphill at 160-163 pretty much “all out”?  If so, that would indicate an AnT of 163ish.

With such a small spread between thresholds, you probably need to do most of your aerobic base training down in Z1, which for you is probably below 140.  As a further verification of that, think about whether you could train daily in the 150-155 range and recover enough to repeat the same workout the next day, and the next, and the next.  Probably not, based on your comments.  So Z2 training is just too close to your AnT to allow training their too often.

I hope this helps.
Scott