Honestly Biden seems forgetful and gaffe prone to me. If you look at his speeches from 10 years back he didn't really stutter and he's always been prone to gaffes. Really, he rarely stutteted when he was vice. Like forgetting someone's name or the state that you're in isn't a sign of stuttering. Same for his slurring. Stutterers don't slur words. He also just seems... dazed, even slightly confused, when he gives speeches now. Who knows though, may be it got worse with age and he actually is struggling again. But I kind of doubt it.