It does seem a bit excessive that you need like 10 dudes for 1 truck, just to operate it. Probably two or three is fine to give it a regular maintenance. Perhaps some sort of mechanic platoons or other units could be attached that would repair trucks and armour on the field. Thinking of which, it'd also be cool to actually be able to create custom models but for that another topic should be made.
But yes, motorized units take like 2x the manpower than non-motorized units and that doesn't really make sense when all they're driving are some simple trucks for transport. Which depending on the truck could take up to 20, 30 or like 50 soldiers, it depends on how you pack them and their equipment inside. In my conscript days, our maximum was 33 men in one smaller type truck. So perhaps designing trucks should take into consideration as to how large the truck is and that would affect the cost and such.
When I was doing my service as signals engineer driver, in my country the logistical department had the drivers who were not on driving duty do all the regular maintenance for the trucks. Naturally there was also external leasing service for all the major repairs, rehauls or heavy maintenance cycles, but all the common maintenance like changing oils, fixing minor electronics or repairing tyres was done by the drivers and there was just one driver per car (actually because of peace time, there were more trucks than drivers, but one per car was the target).
Also common trucks were designed to haul 30 troops plus three officers and personal combat/survival equipment besides the driver and they were the heaviest sort common all terrain 6x6 trucks that could haul up to 30 tons of cargo (without the troops) and also same amount in drawn wagon. There were actually some 8x8 and 10x10 trucks for artillery that could have fitted maybe 8 men more and my licence allowed me to haul up to 50 men by semi-trailer, but that was mostly theoretical as the army to my knowledge hadn't such equipment other than for training purposes as they couldn't go offroad anyways, which was the main operating area. Intercity traffic would be operated by rails or busses anyways, so army didn't really need that capability in the first place.
By that example and considering the mobilized troops would mostly work in non-road wasteland, battalion would be around four companies, which would equal about 500 men (or 1k in the case of this game's double-sized batallions), so they would need around 17 trucks and drivers plus couple more for the immediate equipment that comes along and thus there should be about 20-40 drivers for battalion of infantry and thus I agree the mobilizing shouldn't eat that much manpower, but cause extra need for fuel and cost heavy amounts of IC and perhaps metals in the creation.
So as we know one unit of manpower equals hundred men, the ways to go would either take the manpower need away completely, replacing it with need for metal and consider the trucks simply as equipment driven by the fighting unit or that single creation of trucks would provide 5 sub-units of trucks that can each carry 500 men or similar amount of arty.
One more thing I would like see changed besides the mentioned ones is that as the trucks get Field Testing xp same ways as the other units, you must actually get them either killed or atleast shot on to get them to gain points in the Basic Design Score. Thus I would very much see at the very least trucks if not all units to get one point increase to Field Testing xp simply by taking part in combat. Rarely do you need to let trucks be destroyed to see their weak points or where is room for improvement.