I'm glad you found your groove. I still have remind myself to downshift.Totally true, and I wish this had been posted a few months ago! I always thought that the goal for speed was to shift up to the highest gear and then power through it, shifting down only when you were really struggling. It was puzzling to me that my wife could easily outpace me on her bike, even though she wasn't anywhere near her highest gear. I eventually noticed that all of the hardcore cyclists were pedaling with a much higher cadence than I was, and that it was rare to see anyone on their absolute highest gear.
Lesson learned: shift for cadence, not gear number. Your legs still get a workout and become stronger. I've been doing this for a few weeks and even though it initially felt as if I was cheating by lowering the pedaling resistance, I find that I'm now taking the same trails at one gear level higher (7) and occasionally reaching for the highest gear (8) whereas previously I was one down (usually on 6 and only occasionally shifting up to 7). Whereas I used to always ride on the largest crank arm, I now stick to the middle. It has been pretty exciting for me.
Now looking into going clipless. Bought some used Shimano M324's for cheap (platform on one side, clip-ins on the other so that I can get used to them) and found used mountain-style biking shoes for cheap as well. Got the clips screwed in and already practiced clipping in and out while stationary... it feels both awesome and frightening to be "bolted" to the bike like that. First test will be this weekend.