I’m curious what you’re trying to achieve? Based on “the book,” muscular endurance refers to mainly training your anaerobic endurance. to me, this would mean some sort of interval training for your goals. In your case, I would run intervals of stairs, just to be able to control some things a bit better. Rest should be long and passive. Depending on what you want to do, you may eventually work up to that 3000′ slope where you burn up it in an hour or 2??? But, zone 2 is not where you want to train.
Another word of caution, over stimulating your anaerobic endurance will cause your aerobic pace to drop if you don’t bring your aerobic endurance along with the anaerobic training.