2002 Eclipse 3.0L O2 issues!

Hey Guys, I got my son an 02 Eclipse with a 3.0L auto Trans. The car has about 160K on it. A buddy and I recently changed the transmission while doing that we replaced the exhaust pipe containing the cat. converts. because of the check engine light was on. After changing that pipe the light stayed on, the codes indicated that we had a problem with the O2 sensors on Bank 2....I changed both sensor 1 & 2 on the rear bank, the CEL stayed out for 2 days, now I am getting codes indicating Bank 1 sensor 1 (we have also changed bank 1 sensor 2) I have replaced the O2 sensor with a Bosch Direct Fit (not using the universal O2 sensors) and still have the codes indicating Bank 1 Sensor 1. Could we have gotten a bad O2 sensor (I wouldn't think that would be a common issue) or is there something else that I should be looking for? Ironically, my buddy and I are have a very similar issue with a 1998 Eclipse with the 2.0L Turbo that we are trying to help another buddy fix. Any thoughts or any input from you guy's would be greatly appreciated. My son's Eclipse has not had any engine modifications done, all factory and/or direct replacement parts have been used when repairing the car. We did change the timing belt about 10,000 miles ago.
Thanks in advance for any help with this matter.

Yes - Sometimes new parts are bad!
bank 1 & bank 2 sensor 1 is used for a feed back signal for the ECU to control air/fuel mix.
1) Don't worry about the sensor 2 problem for now, focus on bank1 & bank2 sensor 1 faults.
2) Do a visual inspect on connection and use dielectric grease.
3) Use anti-seize compound on your H02 sensors.
4) Reset/clear codes
5) Monitor
6) How's the fuel economy?

Thank you for your reply! As for your question I can't say that the fuel economy is poor but again it is a V6 and it has a 20 year old nut behind the wheel. I will look into all the items you have listed.
My buddy and I made some progress on the 1998 that was having similar issues, a previous owner made some engine mods and had the bank 1 sensor 1 plugged into the cruise actuator and the cruise plugged into thr O2 sensor. By chance we noticed that the plugs were identical. so that has worked out,
Thanks again.

Moved to Eclipse 2000+ section.