You are experiencing a bad tcc solenoid. This is the solenoid that locks your torque converter. I have no pictures of it. It is located under the side cover of the transmission. Its and easy fix. You need the tcc solenoid and a side cover gasket. These you can get at any gm dealer. The pt# for the side cover gasket is 8688169. There are two different part numbers for the solenoid depending on the application. Its best to have them look it up when you purchase it. It will be either 8689901 or 8689902. Good luck!