check the engine horsepower. Try putting on the one that has the highest horsepower from all available once u do that then there is nothing else to do in order to make u faster.

Also if you have full armor your dd will be slow. If you read the quides then u will notice that you should be using the minimum amount of armor for km.

Good luck

Check the engine before you buy. Don't just buy what's at bottom or top etc.
Most people who complain have bough the submarine engine which is slowest.
Find the destroyer engine, CL engine etc.

You likely have the wrong engine on your dd. It is probobly an SS engine instead of a DD one. Make sure you put on the Heavy DD engine. It will give you the best possible speed for your ship.