Confusing Shift Pattern on 2003 Altima with AT

Here is my story. I just purchased a 2003 Altima S with automatic transmission. For those of you that have driven one, you know the shift pattern is a little unorthodox. I had put about 400 miles on it, and I thought wow this 4 cylinder has a lot of pep. I was concerned at higher speeds (80mph) that the RPMs were too high (around 4500 rpm). It was about this time that I noticed I was driving in third gear not drive.

The car runs great. I was wondering if this could have shortened the quality or life of the engine since it didn't have a proper break-in. According to Nissan, a proper break-in involves 1200 miles at less than 4000 rpms.

That shouldn't hurt it, especially since you weren't near the redline. The break-in period is really just to keep you from driving the vehicle like a maniac right off the factory line. Damage would probably only happen if you kept it at high revs on several days and for extended periods of time. Or if you overrev the engine by downshifting at too high a speed.