I started at 370 miles pulling our 16K 5ver, I did take it easy for a while and it never heated up or acted like it was having any problems. After about 5K it really can alive. I've always been in the break it in the way your going to use it crowd.
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2013 F350 Lariat SC DRW 2WD 6.2 4.30 Gears Air Lifts 50 Aux tank
2003 F150 SC XLT 4x4 4.6L 3.55 gears
2003 HH Premier 35 FKTG