I can't say I hiked mountains last year during my elk hunt, but was around 6-7,000 ft, coming from 100ft above sea level.
For training, I walked 3-4 miles per day M-F, increasing to 6-7 on Saturday and Sunday with a 20lb weighted vest. I did a ton of farmer carrys with 25lb bags at about 150 yards, then turned around and did it several more times. I also did a hike with my brother and his girlfriend in a state park not to far from me that had lots of ups and downs.
The only time I felt like this failed me was when we tried to chase a couple elk that were high up the side of a mountain. Between thick brush and climbing the equivalent of 100 flights of stairs, I was pretty winded after 30 minutes. And, no we never found the elk we saw.
My issue is a badly compressed lower back and suspect knees. I wouldn't try to carry 80-100 lbs on my back. As I got closer to my hunt, I actually dropped my pace and distance to prevent any injury.