The longest uphill in Sichuan and Tibet is about 100 km from Litang to Haizi Peak. But the slope is not that big. In fact, there are many steep mountain roads, such as Zheduo Mountain, Zongla Mountain and Lawu Mountain. One more thing, some tunnels on the Sichuan-Tibet line have not been completed yet. However, the old road is rarely maintained (simply to ensure smooth traffic), so some road conditions are very poor, such as the section from xinduqiao to Yajiang, the section from Yajiang to Litang via Xiangkezong, and the section from Bomi to Lulang (Tongmai Bridge collapsed in early August last year, and two donkey friends disappeared). Most importantly, the elevation of almost all sections of the Sichuan-Tibet line is above 2000, and some sections are above 3000, 4000 or even 5000. This is the most essential difference from riding a watershed. So, according to my estimation, there is about 70% difficulty (average).
If in doubt, please consult again.