TN VISA RENEWAL..Please help

Unless its Management Consulting which is temp in nature so maybe you need to type in a new job description or tell them why they need you after 2 more years for a period of 3 years.
Bear in mind M. Consulting is supernumerary in nature

I have been working on a TN-1 since 2006, renewed each year. Now, I have another job offer that begins on June 14 - - Previous TN-1 expires tomorrow, along with the I-94. What can I do to be still 'legal' in Florida, before my new job begins? Do I need to return to Canada, or is there a way to stay in Florida and send in my application? Any information would be greatly appreciated.

Your short period of being out-of-status will be forgiven when you go to the border to get TN.

You cannot dod a mail-in as you will not have continuous status, which is a requirement for getting a change or extension of status.

Go outside US anytime in the next few days and petition a new TN.

Yes, that's what I did. Visited in Canada for a week with my TN-1 letter presented coming back to the U.S. Now I'm valid for another 3 years. Thanks for the reply.