Sounds like you broke one of the cardinal rules of fighting an F4U: NEVER misjudge his E State.
Corsairs hide their E very well. They're very fast birds with very good E retention, and because their level acceleration and sustained rate of climb are only average at best it's very easy to underestimate just how much E one has. The end result is that F4U 5,000ft below you suddenly zipping up under your bellybutton and ripping you a new one.