The real purpose of the breakin period has little to do with the Jeep and everything to do with the driver. Statistics say that the most accidents happen to brand new vehicles that the drivers are not yet familiar with. Therefore the dealers insist that the owners drive at reduced speeds during the most dangerous 500 miles.
It matters little how many Jeeps or TJs you have owned or driven. In fact the correlation goes the other way, first-time Jeep owners are among the most cautious and drive the slowest. A longtime TJ owner will try to thrash his new vehicle at least as fast as his old one and will experience the highest accident rate.
By all means observe the breakin period. There are a few not-so-obvious items. Brand new tires, for example take a few hundred miles to lose all the mold release compound and become flexible and to conform to the road. So remember to be cautious after every tire purchase, including a brand new vehicle.
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2001 Grand Cherokee WJ
2003 Wrangler Rubicon TJ