○ no need (I've done that several times). Once your TN is approved by USCIS, you get a green paper (that's called approval letter). it has a new I94 number. You can stay in US till the expiration date on that approval letter.
○ you might want to check with ur lawyer. I've done several times from TN to new TN (within US), I never have to get out of US. never from B2 to TN.
○ you are right .. received green paper with a i-94 attached yesterday. just book the airline ticket.for friday. thanks