If the truck has been mainly driven on highway at normal speeds, then the wear on the plugs will be very slight. You could try pulling just one, that is easy to get at, and check it, but I wouldn't even bother. They have installed a long life plug in there, and if truck fires up instantly when starting, if the idle is perfectly smooth, and if you have been driving moderately then it should easily be o.k. for another 10k. Other signs of healthy plugs are that your gas mileage is what it should be, and the engine runs powerfully under all conditions.