Where is the shift solenoid located at on a 2000 chevy Silverado 1500

There is more than one "shift solenoid". Testing is required to find out what is happening -- is it an electronic control issue? An internal electronic issue to the transmission? An internal mechanical issue? A wiring issue? A hydraulic control issue? Too much to guess at. Testing hands on by a skilled technician with proper equipment and reference material is needed.