Hello! Welcome to the site! Thanks for coming! I'm Ron Z. I'm here to provide as much info and insight as I can, to best answer your question.
Looks like there are going to be 2 different problems here.
First, let's do the po171 po174 po135 po141 po155 and po161. When these codes are all set together, the most common problem associated with these is going to be a fault in the MAF Sensor. Before condemning the MAF, let's run an intake air leak test, just to be sure. With the engine
running, carefully and sparingly spray some carb cleaner around the base of the intake. If the engine responds, this is a sign of a leak and the intake gasket will need to be replaced (make sure to visual inspect the manifold itself for any cracks at this time as well). If these all check ok, then move onto the air filter housing, duct and filter element. Inspect the duct for any cracks, holes or loose connections. Make sure the filter box is sealed tightly and correctly. Inspect the filter element and make sure it is not excessively dirty, restricting air flow. If all of these check ok, suspect a faulty MAF Sensor. There IS a "cleaner" for the MAF sensor, however, in experience, it's usually not a 100% fix, and when it does work, it's usually not for long, and MAF replacement is usually necessary.
The P0446 is a different problem in a different system. This is actually a "known problem" and GM has issued a Technical Service Bulletin that states the most common problem with this code is going to be: Replace Evaporative Emission (EVAP) Vent Valve Solenoid Assembly and Add/Relocate Filter Box Using Service Kit.2004-2007 Model Year (Use Service Kit P/N 19207763)
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