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Gatland was in Dublin on Saturday to watch Ireland end England's winning run on 18 games and deny Eddie Jones' side back-to-back Grand Slams.
And speaking before the game to ITV, the head coach revealed just how tough a call he has to make in the back five of the scrum.
"It is about picking the best players who will perform under pressure," he said.
"I think particularly second row and back row - there will be some quality players that miss out on selection that is the hardest thing for us so it is a big challenge for the loose forwards and second rows.
"There is a lot of quality and depth, it is a difficult position to be in but a nice problem to have."
Last week Gatland confirmed the final additions to his coaching staff with Graham Rowntree and Neil Jenkins both on board for the trip to New Zealand.
Now the stage is set for his playing squad announcement in London next month - and Gatland admits he will need players of real character to take on the word's best.
"There is no harder place to go than New Zealand to play against the double World Champions away from home," he added.
"To do that you need to have players who can try and do that and front up when it matters and dig deep. It is not always about pretty rugby but it is what is up here (head) and in here (heart). Those are the big things that really matter particularly against New Zealand."