@yogiskier,
below are your comments in black and mine in red. Many of these things have already been said, so a lot of my post is reinforcement of what you've already read here.
I am jealous of those skiers that I watch cruising down steeper runs in perfect control. I feel like the way that I ski on blues is that I pick up "too much" speed and then end up braking, stopping periodically down a run.
Solution: Picking up speed is a result of not completing your turns. This is a common issue with people who are still building their skills. The solution is to slow down between each turn. Work on slowing down to a crawl as your skis turn to take you across the hill. How you do this matters. There are the good the bad and the ugly ways. Choose the good! A modified version of hockey-stops is the bad/ugly way.
It's also tiring on my muscles.
Solution: Skiing well shouldn't be so tiring. So if your muscles are tired, quivering at the end of the day, and sore the next, you are probably doing two things: skiing while sitting back, and pushing your skis out to an edge. The first is like doing wall-sits, and the second is like doing squats and leg-presses. Good turns don't involve these movement patterns. They involve something more like riding a bicycle or using an eliptical machine, where one leg gets long and the other gets short. An instructor can show you how to avoid skiing with your body hovering over your heels and avoid pushing your outside ski outwards to an edge. That solution will involve making your turns with a long-leg-short-leg movement pattern. The timing is important, and other accompanying movements are too.
I'm tenser than when I'm skiing greens (though I keep telling myself to relax my upper body). I'm guessing that part of it is mental and I feel scared of the steepness?
Solution: Learn the good way to create a turn on a non-threatening pitch then slowly work your way up to steeper terrain. When you are frightened on steeps, it's probably due to thinking your technique is inadequate. That may be accurate. Fix your technique and the fear will probably diminish with repetition of good turns on the steeps. When you get that mental thing happening and your brain freezes, you'll revert to the old (bad) movement patterns of how to make a turn. Most people get in the backseat and do some version of hockey stops, which causes out of control skidding at the end of each turn (on hard snow here in the east). Those skids lead to gaining speed down the hill. And your muscles are getting tired. Go back to the lower pitch terrain to push the reset button to reacquaint your body with how to make a good turn.
Am I working my body the wrong way? Ironically, I like the feeling of going fast to start, but then the acceleration becomes too much - I'm including this observation, because it could be that I'd need to be patient with my turns at the top to be able to continue in control.
Solution: You probably are making Z-shaped turns. We don't have video, so all is speculation, but your descriptions lead to this conclusion. Being patient with the top half of your turns, and allowing there to be a middle part where the skis head straight down the hill for a bit, is the solution. For every turn, you will slow down to a crawl if your skis turn slowly to take you across the hill. Whipping them around is the problem; they can't grip on hard snow when you do this, and they won't take you across the hill slowing to a crawl. You'll skid down diagonally, hoping please for some grip.
I did notice that when I was following 2 other intermediate skiers last weekend that even though they looked like they weren't skiing aggressively, they still kept beating me down the mountain by a long shot.
Solution: Aggressiveness is not the solution. Doing Z-shaped turns more aggressively doesn't work. Making round turns does. You need practice doing these on unthreatening terrain.
I have taken some lessons, but spread out over the past 6 seasons since I started skiing in my 30's, so I've only just gotten out of the backseat. Of note, I don't know how to use my poles, which seems integral to how those role model skiers make it down with aplomb.
Yes, using poles on steeps is important. If your pole plants are mis-timed, you need to fix that with an instructor on non-threatening terrain. Poor timing with poles usually accompanies back-seat skiing. But fixing the pole plant isn't enough to get the feet and legs to start your turns well for a round top part of the turn and an existent middle part where the skis point down the hill. You'll need to learn foot and leg work before worrying too much about pole plants, or you can work on both at the same time. /QUOTE]