My two cents:
fxdemolisher wrote:D1 is very intense (L3 at 23 rounds or L2 at 30) but D2 and D3 fall of very quickly.
I do not understand. If D3 seems easy, you should be able to level up, right? The next level should be appropriately harder. I found D2 and D3 easier, myself, when I was at lower levels (and I started at L1), but ime, that changes at a certain point. As D2 targets strength, you will get to a point where not your endurance, but your strength is the limiting factor. At this point, D2 will become tough.
That said, there's nothing wrong with adding exercises after a workout if you feel like it. Just do twenty minutes rope-jumping after your D2, for example :)
Also, i do D1 on a Monday and will tend to skip if I am out too late the previous night (i exercise in the morning). This is what usually ends my runs on simplefit.
You could adjust your schedule, maybe?