Theres a thud when pressing gas after braking/ slowing down on highway

What is your question?

Its on a 2008 Ford Crown Victoria Police Interceptor. (Aitomatic) I notice this mainly on the highway that if Im driving and say press the brake to turn off my cruise then hit the gas a little theres a thud/ little jolt when it goes back into gear. Im not sure if it does it more when going into a specific gear but I think its a transmission thing although it could be something else completely such as perhaps old, worn engine mounts or bushings. Does anyone know what this is/ could be and if it is a transmission thing like I suspect is this a sign my transmission is going bad?

What makes this problem better or worse?

Usually occurs/ is at least more noticable on highways/ highway speeds