My TB was welding crappy a wile back, turns out I had a poor cable connection. Swap cable from one of the good welders to check. I have had it weld poorly on other occasions because my son would play in the back of the truck and flipped the switches, or move the cables from CC to CV. Take a pic of the front panel as it is set up to weld and post it. Also, if there is a remote on there disconnect it and try.