I used to drink 2-6 cans of Diet Dr Pepper everyday. I HAD to have one when I woke up in the morning. Felt wrong and would go to great lengths to not run out-late night grocery store runs for the next AM, family & friends would have it for me in their fridge's, etc. I had been doing this for over 20years. I would bring stash cans with me everywhere I went. I NEEDED my DDP to function, despite my boyfriend's 6year nagging to quit.
Then during a lowcarb stint a couple of months ago, I read that fake sweeteners can stall ketosis for some people. I was quite miserable doing VLC and decided to ditch the DDP since I was already limiting myself so much in other food choices, plus I knew the DDP was bad.
I cut back a can a day, and then just quit. I did however buy some sparkling mineral water in cans to help replace that carbonated-cold-can-feeling. I haven't even missed it. I can't believe how easy it was. I also started drinking tea for the caffeine boost that I thought I would miss but now only do that randomly. I think most people wouldn't miss caffeine at all if they are doing paleo and sleeping well. It is more like a mental habit/addiction. I would know because everyone I know is DUMBFOUNDED that I quit my DDP addiction.
Just offering this up for encouragement for everyone that quitting the caffeine probably won't be so hard like you think it will be. BTW, I feel much better not drinking diet soda.