As previously noted rpm in any given gear is determined by rear axle ratio, the ratios in the transmission and tire diameter. A tune will alter the engines torque curve and probably increase top end horsepower. IF [ big IF ] the change in the torque curve results in a big increase in low end torque you might be able to stay in 6 th. without lugging the engine, thus avoiding a downshift to 5 th. Of course the tune will almost certainly involve increasing the ignition timing advance which will make the engine more prone to detonation if you do lug the engine. These are relatively small displacement engines that love to rev. RPM is horsepower literally. The formula for horsepower is: horsepower = torque x rpm divided by 5252 [ a constant ]. I agree with others that say let it eat. 2,200 rpm is nothing for these engines.