The 877 miles looks like it could be theoretically possible. Bigger heavier model S did 670 miles using similar crazy conditions (except outside temperature which is hard to 'control') ... crazy though 30 hrs of driving @ 20+ mph. Model 3 is smaller lighter relative to battery size and should get more range.
A Tesla Model S 100D just drove 670 miles (1,078km) on a single charge
A Tesla Model S 100D just drove 670 miles (1,078km) on a single charge