You can get a great deal of useful information by running a TV Fool Report...
http://forum.tvfool.com/showthread.php?t=4 It would help a great deal if you would post a copy.
KGO is transmitting on VHF 7. The DB-4 is an excellent UHF antenna, but it does not cover the VHF band... That's by design. I think you can improve your VHF reception quite easily, but without a TVF report, I'll be guessing.
KNTV is on VHF 12 but is probably doing OK, in part due to higher signal level and the frequency is higher, closer to the UHF band the DB-4 is optimized to cover.