Your thesis or dissertation should have a college reading level for academic work. Proofread in several short blocks of time.
Grammarly contains free tools through its website or a Google Chrome extension. Colorado State University; Proofreading.
Talk with your professor about helping you understand why you make the errors you do make so that you can learn ways to avoid them. If you read through the paper at a normal speed, you won't give your eyes sufficient time to spot errors. Where you proofread is important!
Having another set of eyes look over your writing will often spot errors that you would have otherwise missed. How does one proofread a paper? One of the first signs is when students spell their own name incorrectly or they forgot to use capital letters.
Don't rush through your proofreading process.