Notice how there's no price mentioned.
Given that a used IC semi costs $80K used - which is roughly the price of your Tesla sedan, how much would the Tesla semi cost? $500K?
As for 20% more efficient - it would be interesting to see just how much difference that makes vs the operating cost. 10 MPG is considered good for a semi (fully loaded). Assuming 60 hours/week, 50 weeks a year, 60 mph average, $3.50/gallon - the operating cost for an IC semi might be around $18K a year. 20% savings on that would be $3.6K. Triple that for maintenance and what not - $10K.
$10K savings per year if the vehicle costs 4x or more the price? Non-starter.