Infinite Class Trucks:
     To  get  this  you have to complete the first 27 tracks in single
race mode.

Pro Class Trucks:
     To  get  this  you  have to complete the first 9 tracks in single
race mode.

Dodge T Rex:
     To  get  this  you  have to get first place in season 4 of career
mode in the power division.

Rod Hall Hummer:
     To  get  this  you have to get in first place in all divisions in
career mode.

Shelby Dodge Durango:
     To  get  this  you  have to get first place in season 4 of career
mode in the speed division.

Humvee:
     To get this you have to get first place in the first 3 seasons of
career mode in all divisions.

Monster Truck:
     To  get  this  you  have  to  complete  all 36 tracks on the hard
difficulty setting in single race mode.