alt Hacker NewsA used Model 3 LR cannot do 300 miles of highway driving in almost any condition. Even a brand new one cannot do that. The only way you get 300mi of driving out of a Model 3 is if you drive at 35mph or something, which would be wildly impractical for any road trip situation.
You'd do a good bit better at 35. A realistic range at 65-70mph would be about 250-260.