Apparently, forcing the cable box to put out everything at 720p has rid me of all problems. Also since my original post, I began experiencing HD signals being shown as 16:9 inside a 4:3 480i screen size.... yuck!
The following produce the best results for a Toshiba 46HM95 and a Brighthouse Scientific Atlanta S8300HD:
46HM95 - auto aspect ration - ON
S8300HD - via the HD setup screen, remove all resolutions so that only 720P is selected.
S8300HD - picture format - Auto DVI/HDMI
S8300HD - picture size - normal
Arghhh - I wasn't signed in.