[njsteve]

Is it a GM original ignition switch or a reproduction one? The repros are terrible and the internal "notches" (accessory, start, run) tend to not line up with the position the key is in and it leads to situations just like you described. If it is the original switch then check the column internal linkage rod to make sure the ignition switch box at the base of the column has not moved out of adjustment. This is the plastic and metal contraption with the slider that moves the terminals into contact to activate, start, run, and accessory. The switch box has oval slots for up and down adjustment. They also tend to get filled with dust and crud under the dash and can jam (which may be your issue). I'd remove it and flush it with some brake-clean. Then maybe a light WD40 spray inside to get it to slide smoothly and firmly engage with a "click" in each position. Reinstall, readjust, and see what happens.