I really like the Michigan "mega-orders". What I miss: being able to repeat these orders with different trucks.
So rather than a contest with exp and money depending on time, I'd really like to have a timed task with a fixed XP and cash (honestly, I wont even care if there is no XP and cash at all) but getting a time from first cargo loading to "finish". Maybe even intermediate times for subtasks or "miles driven, average speed..."
Rough sketchup: A standard contest with no time limit or a "999 min" for "gold" if you want to keep it simple.
I think these tasks are quite a challenge and you can work out way better the different performance of trucks.