This is awesome.
I had a lot of fun with this one. The fact that you added a stopwatch to the levels tells me you know exactly who your audience is. The high max-speed of the truck, and the lack of punishment for hitting walls, made it really fun to find a fast way through these levels.
That being said, I'm not sure I agree with the addition of the explosion trailer. I'm not sure it added a whole lot to the levels it was included in. I'd prefer to see a "challenge time" to each of the levels as an alternative, and maybe the "harder trailer" could just be longer.
But still had a ton of fun with this and it's very polished for 48 hours. Great job!