RepairPal Certified shops can diagnose and repair your 2002 GMC Sierra 1500 HD. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Could be several things, need to have someone use a stethoscope to isolate the problem. Sorry that the Converter was not it, did the shop misdiagnose this? If so, why don't they stand behind their mistake?