The white highlight is fine. To get the shadows not to look muddy, contrast need to be increased. This will throw off the exposure so readjust for proper whites.
Thanks everyone. I know it's a tricky negative to work with, but I have no intention of relegating it to the trash bin. Worst case, I can always scan and manipulate it, though I'm finding that more and more ungratifying lately. And if I get nothing good in terms of a print, the learning gained from the experience has been invaluable.
I made a few adjustments. First of all, I think my developer was pooped, so I mixed a fresh batch. I used a grade 5 filter under the lens (7 seconds) and burned in some highlights with a grade 00 filter (4 seconds). This is what I've come up with. There's still no true black in the image -- multiple attempts turned the background to mud. But I managed to get a lot closer and still retain some shadow detail.
Huge improvement. The contrast is much better.