Göran once mentioned to me you know your body is good when you enjoy running up hill. I love running up long hills but learned from that advice not to force it and wait until the body loves it as much as the head. If you feel tired up hill it's a sign your body is not ready to be pushed too hard.
Maybe that's totally irrelevant to how you feel but maybe it can help
I think you (and he) are spot on in this analysis. But the million dollar question; how to reach the up-hill-lovin-feeling in a efficiant and wise way? I consider moderate up hill sessions, a few km with low (constant) inclination, a good way. But its hard to find those trails/hills in stockholm area. Here are jus short steep hills, as for ex hammarbybacken.
I would say no matter the length or steepness take it really easy concentrate on "grund träning" or foundations until the body lets you know it's ready. Then love it!!