When I start the engine, unable to move the gear shift from park. on 2001 Chevrolet Silverado 2500 HD

Have to turn off the engine, but leave the key turned to on position, move the gear shift to neutral, and then restart the engine. Why?

Asked by for the 2001 Chevrolet Silverado 2500 HD
Sounds like a shift interlock problem. Check to make sure your brake lights are working. If not, repair as needed and try again.
Brake lights work. Has to be something else.