The alternator wouldn't have anything to do with either of the problems your having ! The key getting stuck in the ignition could be a problem developing with the lock cylinder . Can you turn the key to the off position an then it won't come out ? Or it won't turn to the off position an then not come out ? There are safety devices in place that won't let the key come out if not in gear an foot on the brake pedal etc... electronic an they do fail . Electronic Park Lock (EPL)/Ignition Lock Cylinder Control Actuator:Linear Shift Assembly: If the vehicle is equipped with a column mounted gear shift, it has a linear shift assembly on the steering column. The linear shift assembly has a cable that runs from the linear shift assembly to the ignition lock cylinder case. The purpose of this cable is to prevent the ignition key from being turned to the OFF position when the transmission is in gear and the vehicle may still be moving. The linear shift assembly cable contains a pin that is spring loaded to mechanically prevent the ignition key cylinder from being turned to the lock position when the vehicle transmission is not in the PARK position. If vehicle power is lost, and/or the transmission is not in the PARK position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column.

Now for the stall at stops , Your vehicle has Throttle Actuator Control (TAC) System ,electronic throttle control or drive by wire ! It is electronical controlled .
There are sensors in the gas pedal an on the throttle body ,they are connected to the PCM/ECM - engine computer with wiring ! There is a DC electric motor on the throttle body , this is what opens the throttle plate . Throttle plates do become dirty with varnish an stuff that can cause idle problems ! There are videos on youtube showing how to clean a throttle plate . How to Clean Throttle Body 2007 Chevy Trailblazer