Man if you are skiing blacks at the resort but want to learn to ski ungroomed better...then....don't ski on the groomed stuff as much as possible, it's that simple. Just stay on the edges. Ski the crappy stuff and try to stay on your feet. Take the line through the trees, or head up to Alpental when it's really nuking. You'll learn a ton this way, and it's just the price of a lift ticket. It's all about logging mileage on crappy and/or deep snow.
You sound like you are past the point where a lesson is going to improve you dramatically (though that is hard to say without seeing what you call skiing). Unless you totally suck and were squiggling down the blacks, you just need to put on a ton of mileage on ungroomed snow at resorts, or on short tours. I recommend at resorts since you can put a ton of laps on quick. It's all about attitude and attacking the slope in a controlled way.
Also, locate the really good skiers and try to follow them (within reason). See how they approach runs with fluidity and confidence. Fall a lot. Hope that helps.