In CoW 1.5, their role is completely different. They would be the ideal unit to be deployed quickly to DEFEND territory conquered by OTHER mobile units, as those units rushed on for further exploits, and the enemy rallied forces to attack their flank or breakout from pockets. Their 'extra' value compared to infantry would ONLY be the ability to be moved somewhere quickly, WITHIN already-conquered territory, and nothing else. In general, the trucks would need to travel in a safe and cleared environment, and once arrived, they would unload to 'become' infantry and use all kinds of common defensive infantry tactics, like 'digging in', entrenching, etc.

In fact, lightly armed resistance/partisan units would make truck convoys a prime target for ambushes in their guerilla-style warfare, because during the transport, the trucks would be extremely vulnerable, no matter what superior firepower was travelling inside them. A truck is a very easy target for almost ALL firearms: rifles, machineguns, high-explosive shells can all take out a truck and those riding in it without too much trouble. They wouldn't drive onto the actual battlefield itself - in fact, that would be suicide.

Historically, in the WW2 era, 'motorized' infantry would basically be an infantry unit, equipped with enough trucks to load everyone into and quickly move them to some critical point at the front, where they would unload and fight like regular infantry.

Call of war 1942 armor cars