2000 LS2 codes

We have a 2000 LS2 with the 3.0 Litre SAAB V6 engine.
The SES light is on most of the time. The Service Wrench comes on
occassionally.
The codes indicate lean fuel mixture on both banks and random misfires. The
computer can't identify which cylinders are misfiring. (Not enough misfire
on any cylinder to set the code for that cylinder.)
The dealer wants to replace fuel filter, spark plugs, plug wiring and
catalytic converter for well over $2,000.
The car runs nice, except for the SES (idiot!) light. There is no
indication of any probelms except for the SES light.

Have any of you had any experience with the LS2?
Thanks