I agree tbat you need to make sure the tailwheel is set up as recomended, as that can make a huge difference in handling. Also the same goes for checking landing gear for being straight (there have been many issues with that over the decades).

But if it were me, and it is a Maule tailwheel (as I suspect it is), just remove the swivel cam plate with the one screw on tbe back of the pivot shaft, and then go out and fly it. If it is now a *****cat on pavement too, the problem is in the tailwheel . Either with tbe setup, or with tbe tailwheel. All removing that cam plate does is disable the full swivel function, the tailwheel still turns with the rudder. That tailwheel has wrecked a lot of Kitfoxes, Avids, and even a few Highlanders. And many pilots thought it was just them, when it wasn't.