Thanks everyone for suggestions. I will have to at least give the blank bale thing a try. I'll have to pay attention and see if I can learn to feel when my arm starts drifting. Also, the suggestion about continuing to push the bow toward the target all the way through shot and follow through is a good one.
The only video camera I have access to is the crappy video function on my digicam, but I can experiment and see if I can see anything. I videoed myself a couple years ago, and that was an eye-opener for me alright. Would be interesting to see if my form looks different these days.
I'm actually shooting a very slightly lighter bow (2 lbs lighter) than I used to. I've been shooting about this draw weight for about 3 years or more now, so I'm not sure that I'm overbowed. Perhaps a little bit, since I haven't been shooting every day like I used to. I used to shoot an hour or more every day, but it hasn't been fun lately, so I haven't wanted to shoot, so I practice less... vicious circle, yada yada yada.
McDave: I tried rock climbing, and it's fun, but I couldn't find steady partners so I sort of gave it up. It definitely compliments those archery muscles, though! One time while rock climbing, someone told me that my good upper body strength was actually holding me back in learning how to use my legs and feet effectively - something that most female climbers learn very quickly, out of necessity. Because of muscles built with archery, I was just hauling myself up, instead of stepping up where practical. Anyway, I'll have to hit the hang board again, especially since I haven't been shooting as much.