98 Deville 4.6 Starting Problems

98 Deville 4.6. When trying to start, sometimes it would just click. After multiple tries, it would start. Battery connections seemed fine, so replaced the starter (under the intake manifold!) Still having te same problem. Is there anything else like a sensor or anything that could cause this? Only trouble codes (http://www.cadillacforums.com/forums/) are O2 codes and 2 codes I don't know about. P1253-H0251 insufficient switches bank 2, sensor 1 and P1133- H0251 Insufficient switches bank 1 sensor 1.

Thanks for the help!!!

Could be bad starter relay....not sure