2018 F150 rear drivetrain noise @ 42mph

According to your explanation, there are a few issues with this vehicle. If you purchased the truck, take it back to the dealer, it is covered by the factory warranty. Let the dealer worry about it and fix it, that's what the warranty is for.

I would not want to be an early buyer of a 10 speed. I think there will be problems for the first few years.

Just a note if you decide to purchase one of these new trucks with an electronic transmission. Ford recommends changing tranny fluid and filter every 100K. That is an advertising point ONLY. The problem is brake in contamination builds up on the solenoids of the valve body causing shifting problems. Only solution when the problem occurs is to change the valve body as the solenoids (7 on a 6 speed 6R80 tranny) cannot be changed individually, and the new body configuration has to be programmed into the computer. After mine was replaced on a 2010 F 150 under warranty, the mechanic said to ignore the 100K BS, drop the pan at 30K, replace the fluid and filter, then do the same every 30K and change the filter every other change. NOTE: the valve body with solenoids is a 1200 buck part. AS F-O-R stated, there will probably be problems for a few years with the 10 speed.

Try test driving the non turbo charged V6. They come with the 6 speed tranny.