Those work great on both my t/a and silverado...I did have to replace one on the silverado because it was doing the same as what you mentioned. Upon closer inspection, the rubber edge that goes against the windshield had come apart from the rest of the wiper. You might check to see if yours have done the same.
99 t/a stalled A4, H&C, suspension mods, TSW Jaramas 20x8.5 & 20x10. 392hp 385tq