When quitting any addiction you have to be absolutely committed. You also have to consider that this isn’t just a caffeine addiction, it is a sugar addiction as well. Mountain Dew, for the longest time, was considered the cola with the most sugar.
You really shouldn’t quit cold turkey because you get horrible withdrawl symptoms. Taper the amount off over a week , but not any longer. Then you will go through a couple days of feeling like crap. Then you have to deal with avoiding triggers that make you drink the soda. For example most people will drink it with salty foods as it makes them taste better. (i love soda as well, ick).
Finding a substitute without sugar or caffeine can also be helpful. Water is great if you can handle it or herbal tea. Or you can drink carbonated juice drinks, some are horrible and others are great.
If you are really just trying to get off the Caffeine and not the sugar you could try switching to non-caffeinated sodas of which there are tons of choices.
Also you might like to know that it takes 32 equivalent sized bottles of water to rid yourself of the toxins in one soda.
What typically makes you start drinking the soda again once you quit??