Trigon sound deadening

I am think about applying a solution called Trigon to the bottom of my Yukon to stop gear noise. The supplier told me I could apply it directly to the outer gear case and transfer case. Has anyone ever done this and if so what were the results. My Yukon has a gear noise from 55 mph to about 59. It drives me crazy. The local dealer said nothing is wrong and he doesnt hear the noise. The car is otherwise quiet until I am at those speeds. Any suggestions?