Thrust Increase
Just a point about the thrust increase heard during the TO run - this is not an indication that reduced thrust had been set at the start.
The engines are never run at the rating which can be obtained by - as Boeing put it - Firewalling the throttles, even when Full thrust is used.
Firewalling gets every last ounce of thrust out of the engines and may well cause irreparable damage to them. It is a last ditch method in dire trouble - as this case appears to have been.