I would either cold turkey or slowly taper off caffeine over the next week, switch to only decaf coffee. Maybe after a month you can have a cup of green tea daily (hits different + super healthy). I only drink decaf coffee now and maybe weekly I'll treat myself to a normal caffeinated latte. At the same time, sleep 8 hours per night as often as possible. You said a few nights you've slept well, it will take longer than that, getting out of sleep deprivation can take several weeks. I understand about the brain fog making the stutter worse. Right now I'm battling unexplained chronic mild dizziness, it's made my stutter much worse since I'm having to mentally deal w feeling like I'm walking on a boat at all times + the usual stuttering copes. But it sounds like if you quit caffeine + get out of sleep deprivation that should get you back to baseline. Btw occasional caffeine seems like it helps the stutter. That effect seems cancelled out when I'm addicted to it, for me at least