Welcome to the Grind!!!
After you complete the main championships you'll have a lot of trucks to get. Too many to remember and I didn't bother counting but here's the route to take to get to grinding.
First, get your favorite truck and upgrade that. But sense Bigfoot isn't in this game get your second favorite truck.
Do the Arena Championship as each completion of the 18 events is about 35-45 min for 22000 CR first place finish and 21600 for coming in first for each event.
For the racing, Just have a T5 truck and beat the easy AI. 2 wheel events only need 3011 points to get the top winnings. Freestyle only needs 11000 points for top winnings. 1200 CR for first with each of them.
If you want to save time then you can throw the Greensboro and Wilkes-Barre races at the start. Get close to second so you still are ranked higher than 8th as with those two the 1 lap you complete is longer or as long as the entire 3 lap series from the other arenas.
After an unwanted amount of time you'll get enough for the rest of the trucks.