Took my 2014 5.0 truck in to shop with 34000 miles...

Took my 2014 5.0 truck in to shop with 34000 miles that has bad spark knock , lower mileage and reduced HP. Tech report : Large amount of carbon build up in all cylinders and bad spark plug gaps on 5 plugs, so Ford replaced all 8 plugs . Nothing was done to take care of the heavy carbon build up or to fit it from happening again other than telling me to replace plugs often and to buy fuel treatment to help with issues ..what a joke!!
My warrantee ends in 2 k and Im sure Ford is hoping the symptoms don't come back until after my warrantee ends. Changing plugs is a band aid to the bigger problem which they are not willing to make right . I have been a loyal Ford guy since 1990 - this is my 4th New Ford truck and will be my last ..not because of product but because of service. The dealership gets money from the factory to fix problems so why don't they fix it instead of losing customers??