I think (a lot of times) we get told a "voltage" that is being read across a load, rather than 'with respect to battery neg and no load'.
12 volts across a coil may not be wrong or bad, just more or less worthless information, since the voltage seen is the voltage drop of that particular load's circuit, not the actual output/input voltage of the control circuit. we would HAVE to know where the probe leads are connected and what state the system is in to have any sort of clue. there are plenty of ev100 controllers that use a "pull-in" and then a (less current) "hold-in" voltage (it does not take as much current to hold in the contactor, as it does to pull in the contactor).
I wonder if, when the OP says he replaced the entire contactor, if they actually got the correct coils, and if they disassembled the new contactor as part of putting it in the new truck, as this problem is far more often the hold-down screw of the contactor moving tips, or the pin hole or pin on the bottom of the armature.