Catch cans are always recommended on LS engines. It's usually the Gen4s that have more of an issue, but older Gen3s will pass plenty of oil through the PCV system, too. Definitely worth a shot!
I like to use a dryer duct brush or baby bottle cleaner brush and plenty of engine degreaser and brake parts cleaner, followed by a good blowing out with the air compressor to thoroughly clean and dry the intake manifold. While you have it off, it'd be a good time to clean the gunk out from the knock sensor wells and add RTV to the seals. If the sensors look questionable, it's worth the investment to replace them. Use AC Delco or Delphi sensors only. It's also a convenient time to replace the oil pressure sensor since it's a real PITA to access with the manifold in place.
Have you ever considered having an oil sample analyzed?
