2021 gmc 3500hd srw 4x4 let rear end

[Zani Koxha]

I just got the 2021 gmc sierra 3500hd regular cab 8ft bed srw 6 6l gas engine,, and I notice when driving over 70-75 I start to hear a hum coming from my rear end is this normal I never drove a 1ton axel as a daily 

[Another JR]

A big part of why the manual recommends speed and towing limitation during a break in period Is to keep the loads and heat generation low on the brand new ring and pinion gears in the axle until they wear a bit and spread out the contact area on the gear teeth. They recommend staying below 55 during the break in period. That can be difficult for users who immediately have to put the truck into full service. You might be getting more noise than you expect because the teeth are not worn in yet. You sure it’s not tire noise?  That’s the noise i hear most in my truck at highway speed. My truck has 2000 miles on it and I have original Michelins on it.