Yes. All vehicles over $5,000 in value, from what I understand.
Rather than slowing things down, truckers would be more useful in helping to circulate the referendum petitions.
In a normal working republic with govt respect for the Constitution, I would agree. In today's reality, your petition will be treated with just so much contempt from the elitists who inhabit your govt.
Truckers can be one of the most powerfull allies any group could have. Truckers can control economic factors on a very specific, local level, or they can operate with regional or national influence. I think that this tripling of licensing fees will get their attention in as much as a truck tag typically costs over a thousand dollars, you can see that this is major coin for the trucking companies as well as the owner operators.
If you get just 20 or so trucks involved in a "traffic slowdown" centered on the state capital, this will definitely get lawmaker's attentiion. This tactic was used to great and immediate effect in D.C. a few years ago over fuel tax increases and increases in tolls on some Northeast highways. If lawmakers can't eat, get gas, or any of the other supplies that truckers deliver on a timely basis, they will pay attention.
I would start talking to the truckers by going to a truckstop and asking the restaurant manager if you could place some flyers/petitions. Truckers and the CB radio will do the rest.
Remember, sooner or later, everything goes by truck.