I had my motor built when I had the TT installed. After 1000 miles we changed to synthetic and retuned the car and it was making about 40 more wtq so my tuner ended up pulling close to 15% of the fuel off the break in tune. I am close to 1500 miles now and I know the motor is still getting stronger - a testament being that my drive side axle broke this weekend.
I don't know if there is a magic mileage number for break in and as others have said the motors are usually run through a 'pre-break in' at the factory these days. I'm guessing your shop is telling you 5000 miles to make sure everything is well seated and that they can get you a good tune without you having to come back frequently.
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2007 G37S [VQ37HR] Sedan 6MT - Fast Intentions Stage 3 TT - @ttv36 #tptoons
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