RepairPal Certified shops can diagnose and repair your 2007 Chevrolet Silverado 2500 HD. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Could be a bad motor or internal t-case issue. Hands-on inspection is needed.
Use this link to find a good shop near you.
https://repairpal.com/repair-shops
Alex