Douglas Mabe

So about 3,200 miles ago i had a 7inch Rough Country Lift kit installed with 35 inch tires and 20x12 wheels. Did not have a problem with it until recently I have a knock when i turn the wheel to the left or to the right. It has gotten worse. So I took it in to the shop that lifted it and they said they have never had the problem before but its what happens when you lift a truck. They are saying its about $2400 bucks to fix this problem. Im not happy at all, they told me before they lifted it that they have lifted hundreds of silverados and never had one come back due to a mechanical issue. My question is, is this due to the lift its self? or the installer? I know rack and pinions go out on lifted trucks but not until years later not 3 thousand miles later.