Slow day in the park. Lactate threshold?

I'm back to my regular pace huffing and puffing to maintain 15.5-16.5 mph up the hills in PP. I dunno what's happened? I have a feeling it has something to do with the way I've been training, maybe pushing it too hard too often, riding too near my lactate threshold all the time. Some folks from the Kissena club group suggested I read this, looks like a good recommendation.

good day in the park

Short ride = anything under 35 miles. For some reason the legs were all muscle today. Swallowed the hill (in prospect park) a full 2 miles an hour faster than I usually do, and wasn't even breathing hard. I typically huff and puff to keep pace. What gives???