Trucks already pay a lot more in tax and regulatory expenses. In my state, annual car registration is $30-ish. Annual registration for a full-sized 18-wheeler is $1350 for the truck and $30-300 for each trailer. They also have to pay annual fees at the federal level which can be $600+/year, and an additional fuel tax on top of the existing state sales tax on diesel which I don't know the rate of right now. All of that applies to every single power unit and trailer in a fleet.
Trucks should be taxed much higher than cars, but too many people don't know or just don't care that this is already the case, and it has been this way since the 1940s.