One thing I do in all aircraft when I am trying to preserve E is to slack off on prop pitch in a dive. When making your diving approach to a target in the 129, cut the pitch back to 45 - 50%. Your airspeed will climb rapidly as the prop is cause far less drag. Near the bottom of the attack, crank the pitch back up so you can grab more air and make the most of your gained airspeed in converting it to altitude.
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