I recently bought a 2017 GMC Sierra with the 5.3 engine.
My question is does the engine require a break in period, and if so how long?
So far it's been about 300 miles and I've babies it so far usually doing 2500 rpm or less. The highest I've taken the engine has been about 3500 rpm.
Also should I do my first oil change at about 2000 miles or should I follow the schedule in the manual?
I intend to keep this truck for a while.....

Not necessary with the engines and lubricants available now days. I have a 2011 that I got off the lot with 0.8 miles on the odo and it passed 160k this weekend.

I think they say no towing for the first 500 miles. That's about it. Guess that's why my 5.3 only made it 305,000. I had to go fishing.

Agreed, not necessary.

When I was in college my best friends granpa bought a new truck a 2008 chevy with 5.3. We were at his house and he threw us the keys and said go see what you think of it. We hit the governor a handful of times from a dead stop pedal on the floor till the governor kicked in with less than 20 miles on it. It was a great truck ever after.

Would I do it with mine? HELL NO. On my last chevy I just took it easy on it at first and easy on it the first few times towing changed oil first time a little early.

I think this is more about the tranny and the rear diff. You don't want to overheat those gears in the diff. One reason that varying speed is recommended.

All the intricate moving parts and seals and bearings etc. in modern engines and transmissions... I just absolutely cannot wrap my head around the break in period have much of anything to do with the gears in the differential.

The gears take a set in the first several hours. I have been told over the years that there should be no towing for the first thousand miles in a new truck. That was also in my Dodge's owners manual.

Our 2004 duramax manual said no speed over 55 mph for the first 500 miles. No towing for the first 500 miles and no towing over 55 mph for the first 500 miles of towing.

We abided by the break in and it sucked. Took a couple hundred mile hwy trip to get 500 original miles on it... people hated us and I probably hated myself a little.

Break it in like you are going to drive it.

Read the manual. Do what it says.

I agree, with the new valve train components and lubricants today, drive it like you always will. The same cannot be said using older flat tappet cams and related components, but that's another thread.

My 17 Dodge I just bought I asked the same question, they said just drive it normally as you will use it, I mentioned towing my boat they said do it, I have hauled the boat wit and without tow haul on there is a difference with it on, not too much mileage difference but some. It pulls very well with the 5.7 motor and 8 speed transmission, it does not pull like my F250 4x4 diesel though but not expected to do so. Oddly the mileage towing my boat is about the same with both trucks, but the Dodge sure does do better not towing.

Drive it like you stole it , pulled my Travel Trailer , 30' loaded to the gills , running 70 to 75 no problem , got 11 mpg , 2017 Duramax-Alison.

Just remember the computer records everything.And they look for any reason to void a warranty.