ran codes , showing # 3 cylinder misfire . on 2001 GMC Sierra 2500 HD

changed plugs, wires and fuel filter and still no change .any help would be grateful . thanks

Do a compression test to make sure the cylinder is intact.
1 more answer
Need to check the fuel injectors. my friend had the same problem with his chevy 2500hd (2001) we pulled the injectors, cleaned them out with chem tool B12 spray and the problem went away. good luck!