All 07's have an O2 sensor in the exhaust pipes up near the head for the ECM. If you replace the pipes with pipes that do not have bungs to mount them. You have two options.
1. Have bungs welded on so you can use the stock O2 or Thundermax Autotune Wideband O2 sensors.
2. Get a PCIII and install it to help run your ECM,it comes with O2 eliminators so the lack of bungs for the sensors isn't a problem.