Hi sea - I have the same issue. I smoked 16 - 18 American Spirit Yellows a day for years, and while I've cut down a lot since I've started vaping, I can't quite seem to quit cigs completely. Whenever I reach for a cig I go through a list -- vaping is tastier, more interesting, less toxic -- yet there's something in my brain that makes me want an American Spirit, and I'm still smoking 5 - 6 a day.
I found this article:
2. Smoking smarter?
which talks about American Spirits as "freebasing" nicotine, so I think it's a trickier brand of cigarette to quit. I've got no scientific information to back that up, but it sorta makes sense after reading the article. And I love to have an excuse, something on which to blame my inability to quit cigs is awesome!
For me, cutting down is really a great start, and I'm taking a sort of "sandwich" approach. I've replaced the first cigarette of the day with vaping, and replaced the last 10 cigarettes of the day with vaping. I'm going to see if I can keep eliminating them one at a time until I've just got that one left, and then tackle that one.
I agree with the folks that mention the higher nicotine content, that's a good thing to try. I also have a lot of 6 mg/ml so that I can vape a ton, keep the mouth occupied, without risking overdose. That's working for me, as well as having a variety of flavors so I don't get bored.