Weighted uphill pack carries will definitely help with your fast packing. Strat with some longish easy (Z1-2) type hikes in the early base period. In the late base period toss in a few weeks of these: https://uphillathlete.com/muscular-endurance-me-workout-water-carries/
Vertical Beast Mode: What Is Muscular Endurance? Why Is It Important and How Do You Train It?
You’ll notice a difference on those big vertical days.