…feverish with an elevated heart rate for 48 hours after.
To me, that sounds like illness rather than post-test fatigue. I would keep your training easy for several days to see if any other symptoms develop.
I would have suspected if it was a Z4 effort, I would have blown up before 30min but that wasn’t the case.
30′ in Z4 sounds about right. Z3 ranges from 1-2h.
My LT was determined to be 172, but I suspect it has to be closer to 167 if I hope to recover quicker from Z3 work in the future.
Five beats is splitting hairs. Heart rate is never that precise. Use 170 as your AnT HR.