What week are you in? It’s suggested to only do the program for four weeks.
You should be doing the following:
Week 1 - 3 supersets
Week 2 - 4 supersets
Week 3 - 5 supersets
Week 4 - 3 supersets
Different muscles have different percentages of fast (low endurance) twitch and slow (high endurance) twitch fibers. Obviously those with a greater percentage of fast twitch fibers will fatigue much quicker and performance will drop off. Those with a larger percentage of slow twitch fibers will be more likely to maintain performance, before critical drop off is reached.
Where is your strength dropping off? In the heavy compound work or the following isolation exercise?
This is a good example of where one can learn a great deal about their body and how certain muscle groups respond differently to different stimuli.
You may find that your quads and chest respond more favourably to heavy weight, low rep, low TUT training when compared to your other bodyparts.