You Might be able to hold this off a bit with a little bit of stop leak but it will eventually need to be replaced.
This shudder is your ABS system checking itself - should do that at 3-4mph after start then never again until next start. Perfectly normal.
Something is moving/shifting in the suspension... when you shift. Okay, enough wisecrack from me. Is this clunk a noise, jolt, vibration? Does it happen when you shift back to drive? Trans fluid full, pink, cool and froody?