It sounds like you’ve done a great job through the base period and do not need to add more vertical. With such a good base what will be most effective now will to add these muscular endurance workouts. Use the instructions to achieve the correct pack weight so that your leg fatigue is the limiter not your breathing. Use a very steep hill. If no hill over 25% then use a stair machine. Go HARD on these for one hour up. Do this once each week.