The owners manual says - avoid driving at high speeds for the first 1000 miles.
What is the definition of high speeds?

 

Anything in double-digits.

Just kidding. I just tried to keep the RPM's at 3.5K and under for the first 1-2K miles. Not easy when the 5.0 comes alive and the Angels start singing at ~3K.

 

Above the speed limit. Don't go past 75 max IMO.

 

I drive one like I normally do. No burn outs or towing. Vary speeds. The transmission is learning how you normally drive, so drive normal.

 

The break in process USED to be very specific and would either guarantee long life or kill an engine quick. These days with these extreme tight tolerance engines, the break in typically occurs a bit quicker. Avoid sustained high rpm (not necessarily high speed), but also avoid sustained LOW rpm, and never, never, never 'lug' the engine. Just drive basically 'normal' but don't hesitate to goose it every now and then, run it to the red line but don't hold it there. Same for the brakes, they need to bed in properly. So avoid panic stops whenever possible, try to avoid heavy use like in mountains, etc. Find a large parking lot on occasion and do some moderate pressure braking. Never 'ride' the brakes.