This has been covered on PUTC several times. No where did I see in my manual about breaking the engine in. The weak spot on these trucks are the rear differentials. This is "Expierence" speaking. I now know of 4 people who have had to have their rear ends replaced, mine was one of them. The first 500 plus miles I kept it below 50 mph. Enjoyed driving around in it, not a problem. Also mentions the first 500 miles of towing keep it under 50 mph. Much harder to do. By 780 miles on the odometer, I had such a howl in the drive train I could not stand to be in the truck. Rear ring and pinion out. Parts back ordered...took 8 days to get the gears in and put in. Then the dealership told me to again use the stated break in period listed in the manual, first 500 under 50, first 500 towing keep it under 50 mph.
The rear ring and pinion gears need to wear in and seat themselves against themselves. When towing a different wear pattern needs to be wore in. Extreme heat is generated in the break in process. My differential housing was so hot, I could not hold my hand on it.
Broker describes the trucks he uses for towing 53 ft long trailers loaded as having a system he sets up which is a differential oil cooler mounted in the bed of his trucks.
I have also talked to two D/A owners who told me they drove their trucks from day one in the way they would use them as long as they own them, and have not had any differential problems. Just my opinion. (The differential repair was covered by the warranty and not listed on the repair ticket, but I saw a ticket listing the repair cost at over $1800. .)
Edited by: cloudytown