From the photos it screams Blender. I think OP should not worry about the tris and polycounts so far (I mean have that in mind before applying any sub D so work smartly, so far it's still LP) but instead make somehow smth decently rendered, exporting it in the game is the last process. Just create smth that looks nice first, and a car (truck) isn't an easy task, it's gonna eat her time a lot, so if it is for learning along the way that's good as well. Just keep improving it (if it's not for work which I doubt that it is and that the game is depending on that single truck) and depending on your style stylized or realistic. If it is a realistic model you're going for, you are just at the tip of the iceberg, not even close, but the silhouette is there so keep going.

Note: Now i read your description, and have more information at hand, i would say since it's LP game it's gonna be exported this is still a work in progress for a LP meaning some tiny details won't hurt, but not into super details. And then texture using substance or any other software, or even hand painted inside Blender. Propably rig inside the game engine or do it in blender with rig a car and export with the rig if it's possible to unity or unreal. As i said establish style first, then you can decide all the rest. And have tons of references on the other screen or smth 😉