I bought some Shooter's Choice Lead Remover this afternoon. It appears to be working. The patches are coming out black. The fouling seems to be breaking up, though I've still got some work to do.
Can't really figure out why it's been so difficult to clean this time. My guess is it's the Federal Truball slugs I used. A reviewer at Cabela's said they "...leave a heavy lead smear in the barrels that is the dickenns to get out...."
I think I'll second that.