I cut back on soda for two reasons - 1) my weight varies pretty linearly with my sugar intake, and I've been getting a bit pudgy of late. And 2) the caffeine prevents me from sleeping well. I can't say for sure if the drop in soda intake is responsible for my feeling of well-being but it certainly is easier on my wallet.
I cut back from 4-6 sodas a day to zero for a little caffeine-free experiment I ran on myself. I was drinking no sodas for about 2 weeks.
I felt no different (after I quit having caffeine headaches, that is).
Thus, in my opinion, your difference is (very much nearly) all in the fact that you're now getting enough sleep.