Ah Ha!

I feel dumb for not figuring it out before now. Over the winter I made some TT position adjustments, but nothing drastic. I lowered my bars about a centimeter. And I switched stems - same length and angle, but went to a Thomson stem, which has a much narrower witdth at the handlebar clamp than my old one. When I was switching stems, I thought, 'this would be a good time to flip the little clamps that hold my aerobars to my base bars.' That will allow me to move the aerobars closer together and narrow my position.

So I did both. I added a narrower stem and flipped the clamps. I used to be able to sit a water bottle on the top of my front tire while warming up on the trainer. My aerobars were just the right distance apart and just the right height above the tire to hold the bottle. After the adjustment, I couldn't even come close to getting a bottle between the bars, but it felt ok, so I went with it.

Well, I think the narrow arm position, while aero, I'm sure, limited my leverage at the front end and drastically reduced my power output. Think about trying to crank out lots of wattage if you can only grab the stem on your bike with both hands while pedaling. That's an extreme example, but it's sort of what I was trying to do.

I haven't done any power testing, but based on how I felt on my first TT ride after widening the bars, I think I'm onto something. Wider bars, 1cm higher bars, and seat forward 2cm to open my hips a little more: hopefully those changes will combine to bring my TT mojo back. I hope so, because it really sucks being slow.