Swim Improvement

I've been feeling like I've been going nowhere fast with my swimming lately. I would just get exhausted and feel like I was dragging most of the time. Could have been the diet I suppose.
Well at last night's class we were racing 100's on 3:00. That is much more rest than we typically get. With these races what typically happens with me is I do well on the first one then lose 5-10 seconds on the following races.
So I was surprised last night when the coach challenged me on the 4th set. He wanted me to swim 1:37 or better. I had hit the 50 mark at :44 the previous sprint. I forget what my final time was 1:40+ probably. So I had to really dig to get faster at this point.
One thing I do on the shorter sprints to shave time is breathe every 4 as long as I can stand to do that. With the faster arm turnover it's probably not too far off from every 2 with the longer stroke. I'm not sure if I even make 50 going every 4 tho'. Then to try and push this one faster, once my arms felt like they were slowing somewhere in the 75, I pushed my legs and kicking as best I can (take what I can get). I finished 1:37.8 which matches my best time from back in January, but this was the 4th sprint so I'm calling it an improvement.
I had taken my electrolyte capsule before class and also decided to take my bike bottle full of gatorade 24oz (made from the endurance powder). Typically I take half as much gatorade. No cramping again this week so I'm 2 for 2 with that. The trouble was that I couldn't sleep when I got home. So I missed my swim class this AM. If I had decided to go, it would have been on about 3 hours of sleep, that can't be productive. Not a huge deal. I just think this AM would have been a technique day and I like to be reminded what I'm doing wrong.