I have a 2000 Z71 and last winter my wipers were frozen to the windsheild and the wiper switch was on when I cranked the truck. Ever since that morning my intermitent wipers no longer work. The wipers will work on high speed only and will not return to the bottom when I turn the switch off. I have to time the switch with the position of the wiper arm or it will shut off in the middle of the window. I have checked the fues and it is fine. What else could be the problem ? Thanks!