I watched this when it was pretty new and already it's fading in memory. I think the gist was the N model was boosted to this power level at lower elevations for 15 minutes. It's interesting 1780 HP only got it 378 mph when the early 1100 HP Allison was rated around 360 mph(possibly only with the lighter Tomahawk planes with .30 caliber guns). It was still a draggy plane that lacked the power at high altitude to benefit from the thin air up high.
That power down low should have helped it a lot in climb until it ran out of air.