Need help with shifter problem
 

Hi new guy here. I need a little help in figuring out the correct part I need. Let's start out by telling you what I d rive. I have a 2005 Chevy Silverado 1500 5.3L V8 4 door. I love it awesome truck. My problem is with no key in the ignition I can shift the truck out of park but when I start it I do have to press on the brake to shift it out of park which is correct. My question is it the shift interlock or some other part I couldn't really find info on my problem. But I knew you guys could help me Thanks