GM-GMC: 1996 GMC Suburban 5.7L loss of power, service engine soon light goes on and off, gmc suburban, oxygen sensors

Question
Hi Harry, I have a 1996 GMC Suburban with 97K miles.  The service engine soon light appears when climbing hills and it seems that the engine has less power causing the problem.  The light will extinquish if driving on level ground but the power still feels to be less than we were use to having.  I replaced the spark plugs and filters (fuel/air).  No apparent change.  Was wondering what things to look for that might be robbing the power and causing the service engine light to come on? We brought the car to a dealer for the service engine soon light and they told us we either had an O2 sensor or catalytic converter going bad.  They wanted to charge us quite a bit and had no guarantees.  The car has 4 O2 sensors but I wanted to get another opinion before replacing more parts.  Thanks

Answer
I would take the vehicle to an auto parts store where they usually read the caodes for free.  That might help pinpoint the problem.

Oxygen sensors fail and are usually good for about 50,000 miles.  It would not hurt to change the sensors.  The same is generally true about the catalytic converter, but the converter does not cause the "Check Engine" light to come on (unless it is plugged up).