On thing to remember is that TSS is based off IF, and as stated above IF is NP / FTP, so it's the NP that matters. A steady high AP slog is going to be worth less TSS than a ride with a lower AP but more "spikey". Also the IF term in the TSS calculation is squared so just being a little lower makes a huge difference. For example an hour at 60% is only worth 36 TSS, 75% is 56 TSS, and 90% is 81 TSS.
Edit: also elevation basically lowers your FTP.
Thanks. Just reinforces that I hate this ride. Saw one of your club mates up here though, I think.