2003 Silverado fault codes PO449 and PO455

I have 2003 Silverado 2500HD. Have OBD fault codes PO449 and PO455. I've been told its a emissions valve malfunction.

I have no manual and am new to this truck so not to familliar with locatios of components.

Also have an intermittent squeal that increases with engine speed, At first I thought it was the brake pad squealers but still hear it at a complete stop. Serpentine belt idler??

Any help would be appreciated
Silveradorob
I did an 03 recently with code po455 and it was the evap vent solonoid valve.The valve is located underneath by the fuel filler hose over the fuel tank, about $25.00 from gm.Only way to know for sure is with a scanner and a smoke machine,but this seems to be a common problem on these trucks.