Jason,
I have/had the same issues and am now 7 weeks into a serious effort to work on it. A few things that I think have been working for me are hiking with a 20 lb pack really slow uphill and using a treadmill set at 12% incline (that is as high as mine goes) and walking 2-3 mph. my running economy is really bad an the second i break into a jog my HR goes through the roof, I know i need to work on that separately at some point. I will typically get on the treadmill for my hour easy aerobic base and start out around 3 mph and watch my HR and as it drifts higher than I want I just decrease the speed by .1 mph or the incline by a degree. At first this felt super lame and I always erred on the side of too low a HR and made sure I was breathing easy with my mouth closed. I have seen significant improvement in my power output at a 150 BPM HR and nose breathing in my hiking, cross country skiing, and split-board climbs, usually lagging a bit behind my friends but with a significantly lower HR and way less fatigue. the treadmill routine still feels lame and once the weather gets a bit nicer this spring I plan on setting aside a small part of my routine to train running economy but not at the expense of my zone 1-2 work.
