Were you paying cash or EZPass? The Delaware Bridge is notorious for overcharging RV'ers EZPasses. One of the very few, no, make that the ONLY place that I put the EZPass in the foil envelope and pay cash! $8 is their going rate for a passenger vehicle towing a two-axle trailer.
If you paid cash along the trip, then you likely had a toll- taker or two who didn't bother to look at their axle count monitor, and just charged you for the truck. That sometimes happens when it gets real busy.....
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter