x2 on fan clutch. See if the clutch is turning the fan when the engine is hot and at idle. You could also have a bad water pump - look under the truck to see if you have a trail of rusty water from the weep hole at the bottom of the water pump. That rusty trail indicates a failed water pump.
I would only use a AC Delco fan clutch if you need one - about $100 at the oem vendors, the last time I checked:
www.oewarehouse.com
www.oehq.com
www.davesauto.com
www.gmpartsdirect.com
www.rockauto.com
Get the GM part number for the clutch and search Amazon and Ebay also.