Dave,
Speech recovery varies greatly across different patients. I only had the right side neck dissection and it really affected my swallowing and speech, so I can only imagine how you feel with both sides treated. You just don't realize how many of the neck muscles are involved in speaking and swallowing until they don't work correctly. I highly recommend a speech therapist in your case.
As for the pain, ask you doctor. I did not experience any pain after the normal healing time of the surgery. Radiation? That is another story.
Take care,
Jim