The SCT website toll calculator I reference above . . .
http://aplicaciones4.sct.gob.mx/sibuac_internet/ControllerUI?action=cmdSolRutas
is where you can find out what the tolls will be on your route. And the picture I gave the web address just above will show you what the sign coming into many of the booths may look like. From that you might be able to figure your tolls using the calculator.
I can only tell you what I understand the rates to be based on the calculator. Based on this discussion it is clear that there may be no way to know for sure. The rates do change - though not by much. Then the collectors may see you as different things. But I do think the dually is seen as a truck in Mexico.
The calculator also shows what they charge for trailers. One of the problems is one collector could see you as a 4 axle truck while another could see you as a two axle truck pulling a two axle trailer - and possibly still another could see you as a pickup pulling a two axle trailer.
You can also learn where some of the more expensive tolls might be a learn if there is a reasonable way to get around them on decent roads in an acceptable number of miles.
To get more specific you need to ask those who have taken your specific planned route while driving a vehicle similar to yours - and as several (including me) have stated here - one day you may go through the same booth and then on another day be seen as a different vehicle.
My guess when they show the trailer rate is that applies to a trailer being pulled by a car or pickup. But a 4 axle truck is like a semi tractor trailer rig so if they say you are a truck then if you pull a trailer that should be the same as a 4 axle truck - just a they would charge a semi with the same total number of axles.
But what I think - or what others here think - could differ from what the toll taker in any particular booth may think. Personally I would prefer that they see me as a 4 axle truck - and in our case a 4 axle bus - unfortunately they usually charge us as a bus towing a car which costs more - though we do sometimes pay the 4 axle rate. You may never know for sure until you get in the booth.