That happened to me too, years ago on my Hemi GTX when i owned it.
What i did to fix the stripped thread problem, was to strip the transmission down to the bare case, and bring it over to an industrial, machine, welding, shop here in town.
They bored out the area of the case, and pressed in a bronze bushing, then drilled and taped the bushing to the thread size of the switch.
Don't know if you have to go to that extreme, but that was the way out for me.
