Step 5 - Underwater Pull
The final step of this progression adds the kick.
A very important thing to remember when adding the kick, is that instinct will try to take over again. You will feel yourself slowing down, especially when you start to recovery the arms. Instinct will tell you to set up a BIG KICK as soon as you can. Just remember, the bigger the kick, the more resistance, the more you'll slow down, and you'll be asking your kick to reinitiate momentum... which is really tough.
A better idea is to delay the kick so most of it's recovery is done AFTER the hands have started to pierce the water forward.
By delaying the recovery of the kick until the hands get near the shoulders or under the chin, you'll only have one of the two (arms / legs) recovering at a time, minimizing the amount of resistance you're creating.
That delay can also add a bit of panic in the athletes mind, RUSHING the kick to finish it in time, which hopefully means it's just a bit smaller, creating less resistance, which can maintain more momentum.
It's all a game of timing and balancing the amount of resistance you create with the amount of momentum you maintain.
Keep experimenting and figuring out when to initiate each step, how long to pause between each, and always remember... it's not about how far you go, it's about how fast you get to the other end.