To add to the previous replies: Delphi/AC Delco 02's are the best.
Also what brand fuel pump did you put in? Again Delphi/AC Delco is the best. If it's an Airtex you may have issues with fuel pressure, so that also needs to be checked regardless of what brand the pump is.
For now I would believe the O2's until you can eliminate all other issues that would trigger these codes. Both the P0131 & P0151 indicate a lean condition on both banks from the upstream sensors.
Typical reasons for these codes are:
1. Low fuel pressure.
2. Vacuum leaks.
3. Exhaust leaks upstream of the O2 sensors.
4. Bad MAF sensor.