One more thing that jumps out for me is according to the tvfool report for zip 33410:
http://www.tvfool.com/?option=com_wr...90383236229ff3
It shows NBC on real channel 12 and CBS on real channel 13. I hope that is just wrong data because with them both from the same location like it shows, there will be a lot of co-channel interference which would explain why you have trouble with those channels. I'm surprised to see that as usually there is more separation than that.