I don't think it was ever actually an official US Truck Route, rather it was merely a truck restriction that forced trucks to take a different route. I've included an image from street view that shows what I'm talking about. Unfortunately, the only imagery of the signage is from January 2008, so it is quite blurry, but the sign says "No trucks, buses, rental trucks, or trailers on US 93 over Hoover Dam. Use AZ 68, NV 163, US 95." This is located on US 93 NB just south of the interchange with AZ 68, and the signage had disappeared by the time the next street view imagery was taken in 2011. Anyway, the signage isn't so much a bannered US Truck Route but rather a truck restriction with a recommended route.