GM has an issue with these. They clog from dirt and set the evap system code. They give you a kit with the new vent valve, hose and a filter and relocate the filter over the trans.I still would get the codes checked, most parts places will scan for free.
Bulletin No.: 02-06-04-037E
Date: April 09, 2009
Subject:DTC P0446 (Restricted/Blocked EVAP Vent Path) Set, Check Engine Light On (Replace Evaporative Emission (EVAP) Vent Valve Solenoid Assembly and Add/Relocate Filter Box Using Service Kit)
Models:1999-2007 Chevrolet Silverado (Classic) Models1999-2007 GMC Sierra (Classic) Models2007-2009 Chevrolet Silverado Models (Excluding Hybrid)2007-2009 GMC Sierra Models (Excluding Hybrid)
Supercede:This bulletin is being revised to add 2009 to the models. Please discard Corporate Bulletin Number 02-06-04-037D (Section 06 - Engine/Propulsion System).
Some customers whose vehicles are operated in dusty type environments, such as farming or mining off-road type applications, may comment about the illumination of the check engine light, with a DTC of P0446 (Restricted/Blocked EVAP Vent Path) being set.
Dirt and dust intrusion into the EVAP canister vent hose assembly, resulting in restricted air flow, may cause this condition.
Correction (1999-2007 Classic/Old Style Models)
After following the published SI diagnostics for P0446 and determining that the EVAP canister vent valve is the cause of the MIL light, replace the existing EVAP canister vent valve assembly with a new assembly. This new assembly is a sealed unit that is designed to be vented through a remote filter box. To ensure correct installation, follow the procedures below.
1999-2003 Model Year (Use Service Kit P/N 19152345)
basically you can locate the vent valve and breather where you think it would be protected. they ask the tech to use long hoses.
here is the new vent valve
here are the parts
I HAVE ALREDY CHECKED THIS