Hello there! Speech therapist here. Not being able to say the “back sounds” such a /k/ and /g/ and replacing them with a more forward sound like /t/ and /d/ is a phonological process called “fronting” and it is usually suppressed by the age of 3.5. Concerning the stuttering behavior, early intervention is always recommended. You are the parent, and ultimately, if these things concern you, then reach out to a local speech therapist in your area and get an new speech-language evaluation for a proper diagnosis. Good luck!