Have you considered replacing the bar and stem? some of the current components from better companies

have the torque specs engraved around the bolt in question.

If you have arrived at a fixed location, loc tite Red on the bars clamp will hold them better

cannot say what the torque spec is , size of bolt, [you can find general torque charts on the web] quality of the steel is un known and if threads are cut in aluminum.. (there is a different torque for dry and greased threads too)

the 'GMC' brand is just paint , someone else, some big box type supplier,
made those, in Asia.. no surprise there..