High-five!! That's a true fitness accomplishment! If you're truly giving the intervals your 100%, you should always find this workout challenging, and even stumble through it a bit. It's been part of my rotation for 2 years, and even though I no longer have to modify, it seems like some part of my form could always use improvement. There's always something to strive for, and that's what keeps it interesting.
Good work!
Sandra