My 2000 K3500 has developed a horrible shake in the front end. From about 30 to 40MPH if you hit just the right bump (and it seeem to be getting less picky about the right bump), the steering wheel and front wheels shake back and forth. I have to slow down to make it stop. I've taken it to an alignment shop 3 times and nothing was found to be worn in the steering/suspension.
Any hints??