So the shudder occurs right at 25 mph, or constantly as you're slowing down, or intermittently? Both of my cars with the 4T65E have over 100k miles on them and will give a bit of a clunk or shudder when they downshift into 1st while coming to a stop. I don't know if it's normal or due to components wearing out, but either way, it hasn't caused any major issues for me.