Torque will kill a gearbox more than power, most diesels are not going to exceed the RPM limits of the bearings and gears in the gearbox.

In a gas engine you typically have less torque for the same horsepower rating, so a 300hp gas engine will be much easier on a transmission than a 300hp diesel, which will typically generate close to twice the torque.

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Gone to the dark side

- Jeff