No, It was born a 550. We got the truck 5 years ago with 400,000 miles Now it has 889,000. I put almost 1/2 a million on it. John

 

You can contact Cat when it reaches 1 million miles and get a official cat certified certificate.
Had one customer where I worked that got one.
He had a Pete with a 3406B ATAAC engine.

 

I forgot to say we overhauled it with a Cat Platinum kit at 600,000 due to blown head gasket. It has the two turbo's and the annoying actuators. To bad it's not a 6NZ.. I'd rather drive a Cat than a Cumapart or a drippy Detriot any day . Love the torque...John

 

In my opinion the best Cat engines were the 400 WJAC and then the 425 WJAC. Cat use to have a red head gasket that never failed. When you did a rebuild the red one was no longer available, then head gasket problems showed up.
I will agree with you also about the 6NZ engine.
Long story short. Cat use to paint their truck engines white and later yellow. I had a guy swear that the white ones ran better than the yellow ones.

 

I remember the white ones-1673 &1693 in the 60's-70's