Where is the thermostat located on a 1998 Chevy pick up?

The thermostat on a 1998 Chevy pickup truck is located under the intake manifold. This is a common location for many vehicles. You'll need to consult a repair manual specific to your engine (e.g., 4.3L V6, 5.7L V8, etc.) for precise instructions, as accessing it requires removing various components. It's not a simple "pop the hood and there it is" situation. Be prepared for some disassembly.