Congratulations on using Eben's productivity techniques. I often use the 60/60/30 method (was that in the video - I didn't check?) as a way to box my time effectively.
If you are running out of steam then that is probably occurring because you have some problem solving to do. We are creatures who want instant gratification and when we have an impulse to do something we want to take action immediately. However, if there is further problem solving involved before we can actually take action then we feel blocked, frustrated and even disappointed. This is when procrastination strikes.
After you initially run out of steam, make the next session a problem-solving session. This means that you accept that you can't launch yourself into action and instead will work out what you have to do to accomplish the next task. It might require creative thinking, but often it just requires more preparation and organization.
I have my own device for doing this called a 'How To Do' list and you can get a simplified version of it here:
The “How to Do” List
I've recently finished writing a whole book mostly dedicated to this problem. Write to me and I'll give you more details on that.
Best regards,
Nick