My friend. I have the same problem like you have and the same SUV with an 6G74 3500cc engine and same year; the only diference is that hace 230,000 miles. When I stop at a traffic light at idle speed and wait for about a minute its starts to smoke. My mecanic told me that I have to change the the piston-rings and the valve seales. There is something curios when the oil amount in the engine drops from 4.7 Liters to about 3 liters the smoke disapears, so that tells me the its more posible that the piston rings are the problems and not the valve seals.