chain jumps/skips, but parts are ok!
 

here's the deal: 2005 C'dale Bad Boy, 9 speed.
Lately, and quickly getting worse, the chain jumps under pressure. The chain and cassette have several thousand miles on em, but are not worn out! I get exactly 12", pin/pin when I measure the chain. The tops of the sprocket teeth are square. (I take care of my bikes) It happens in 7th & 8th gears, mostly 8th. (Of course, these are the two I use most often)
What else could it be?

The valleys are probably worn and elongated.

That doesn't really sound like a hanger alignment issue to me, but I'd have it checked anyway. In fact, anytime that a rear derailleur doesn't respond to normal tuneing processes, the first thing that I do is check the hanger alignment. Most of the time that fixes it.