Looking at your two hour climb:
If it was me, I’d do a Friel 30 minute or a longer max effort test. I’ve always done my longer max effort tests similar to Kolie Moore progression 2 or 3. Just go out and do a long hard max effort push for ~40km / ~25 miles if you have a course (or inside).
Like you I’ve seen lower ramp test estimates, and without going into detail it can be an expected result because TR uses 75% of max aerobic power (the ramp test actually estimates max aerobic power / 5-min vo2max, not FTP).