Hello fellow procrastinator! You sound just like me! I have a 4.0 gpa as well, but I can be the worst procrastinator ever at times. I've found a couple things that help me though, so I shall share them with you!
One thing that helps me is to grab a note card or something, and write down everything that needs to be done for homework for the day. It's like it helps me put everything into perspective and to realize just how much needs to be done so that I want to go ahead and tackle it all right away. And then I plan a reward for myself for getting it all done. It's good to have a goal and something to look forward to if you can get it all done within a certain amount of time. You could reward yourself by watching a movie after it's all done, for example, or by going somewhere fun.
Also, another thing that might help you is to set deadlines for assignments for yourself before they are actually due so that you will be ahead of the game. So if it's due on Sunday, give yourself the deadline of Friday.
I hope you find some ways that help you with the procrastination issues. Good luck!