I've been dealing with a knee injury myself and the doctors have diagnosed it as patellar tendonitis. One main cause they say is pushing too hard rather than spinning up hills or even on flats. I'm having to adjust how I've ridden my bicycle for 20 plus years. Like you, I'd rather pedal hard than pedal a lot of times in circles and go nowhere. It's been a struggle to change, but I know my knee will be better off.