Ahh - ok, 1:50/100m sounds much better. That's actually a better than average pace (and streamline) for triathletes. It's pretty hard to swim 3min/100m - a lot of wasted effort, certainly not effortless. So possibly the 2000m in an hour includes rest?
A 1:50 pace at a tempo of 1.0 or 60spm would put you around 22-23 SPL in 25m pool - assuming a 5m glide off the wall. Is this where you were before coaching? If not, what changed?
You noted you are swimming in a suit - wetsuit?