I have no doubt, that on an engine dyno………with solid lifters in the engine, the OP’s engine wouldn’t produce a dyno sheet that had the curve nose diving at 6k.
That might even be possible with the “best of the best” HR lifters.
But is it a nose dive ? @ 112 mph the engine is pulling strong, about 20 mph passed engines peak hp (94 mph), at 116 mph it's definitely off the gas.
So by 112 is still pulling, between 112-114 there's a slight drop could be valve float etc.. At 114 it drops a 150 lbs-ft instantly (valve float ? letting off throttle ?) then by 116 there definitely off the throttle.