Tyler,
Thank you for the clarification.
Muscular Endurance is same as Z3 weighted hill climb. Given your goals carrying a heavy backpack up a steep trail would be recommended. Your pace should be limited by the backpack weight/burn in your legs and not your heart rate. You might have already read the UA articles on ME, if not would recommend reading this one.
For the long Zone 1/2 workouts on a steep trail, you will end up hiking when you are carrying 10% body weight.
Hope this is helpful. Wish you the best with your alpine objectives for this year.