So, I'm going to float a theory, because I have a second vehicle being involved just to drop the two off doesn't really make sense when they could theoretically just as easily have dropped off the truck/trailer nearby and driven Tim's truck straight into that in a secluded area in order to avoid detection.
MOO, I think the reason they weren't worried about people seeing DM is because maybe the second vehicle was there in order to stage a carjacking. That would explain the need for at least two people in the second vehicle as well. One of the guys in the other vehicle to force TB out of the passenger seat of the truck, and order DM to drive away "at gunpoint" and a second one to drive the second car from the scene. Then they'd have had the truck, be looking for the mysterious carjackers, and nobody would suspect the rich kid who doesn't need to steal a truck had anything to do with it. But things didn't go as planned.
Yes they might have pretended to do some type of car jacking or pulling over the vehicle...multiple possibilities.