Nissan Titan Crew Cab 2005 shimmy

There is a vibration that starts at about 43 mph and disappers at 48. I thought it was tires, but I’ve had them rotated, balanced, and finally bought new tires. Nothing helped. The dealer plays dunce on the topic. Should I worry about catestrophic failure

Have the tires rebalanced and check the alignment as long as it is not related to braking. Does not sound catastrophic at this point but sure worth getting looked into.