Engine Belts And Pulleys problems of the 1997 GMC Yukon

Engine: a spark knock has existed since the vehicle was purchased eventually getting to the point that is was very noticeable even at 60 mph on level ground, continually. Dealer replaced several computer components and eventually service the heads and intake by removing and cleaning carbon. 3,000 miles later the problem is beginning again. Gas mileage has suffered to 3 mpg less than when originally purchased. The drivers seat base had to be replaced due to loosness. A/c idler belt tensioner replaced. Power steering hose leaked. Poser steering control would be lost in right turns and valving had to be replaced. A/c does not cool adequately after engine was last serviced by removing heads and intake, reported to dealer and they said there was nothing they could do.