Well, one place to start is: ignore killing machine. There is a microscopic gain from timing it in a way that no human being could ever manage, and a loss from trying to time it otherwise. Let it go on whatever comes up next in the rotation, don't stress about it. Heck, I turned off the damn notification so I didn't feel like a loser every time I got it "wrong".
I see you are 550, so you might find it beneficial to head to the "mastersimple" rotation where oblit basically just drops out of your rotation entirely. Focus on HB/FS/PS and go from there. In my testing no practical difference in performance was observed at 540-ish, and I actually *gained* DPS from this at 550 to 570. (It also means that "wasting" KM can't happen any more because only FS will consume it.
You might consider plague leech, which as DW frost you can pretty much hit as another "gimme some runes" button any time you want, since disease application is rotational for you. If you use non-macro Blood Tap, pick any other talent, though RC or macro-BT would probably be optimal. BT is a gain when manually managed *correctly* and a big loss when not managed correctly. For a non-trivial number of people *cough* like me *cough* it turns out that you make mistakes just often enough with non-macro BT that you are better off not using it. That gain is easily eaten by rotational errors or delayed consumption. :/
Otherwise, honestly, your described rotation sounds fine, so ... I don't know. Unless you run conversion or something, it seems like you should be delivering more than you do, and without logs it is hard to say what the right fix is. Maybe if you are worried, try something like
Bitten's Spellflash: DK which will "recommend" the current theorycrafted rotation for you.
Like any tool, it will not be more than 80 percent right at the best of times ... but getting to 80 percent seems like it might be reasonable to, y'know, confirm that you are using things right. That helps ensure that you are getting it basically right. (That specific addon I suggest because it does follow the current best practices for full and mastersimple rotations, so against patchwerk / a target dummy, it will guide you correctly. In the real world, yeah, not so simple, but whatevs