Installing a tuner on a diesel or gas engine will increase wear due to the additional HP and torque produced, pure and simple. How much is dependent on the tuner settings, other modifications made, how you drive and maintenance performed. A non turbo charged or non super charged gasoline engine will have a marginal increase in rear wheel HP/torque just from adding a tuner. It might change the transmission shift points to make it seem like the engine is performing better which generally decreases MPG...just my 2 cents :-)