Hiteck 7950TH or the JR9100HVT are some serious torque monsters, and for the Cenchain trucks, that is what I would put in it. These servos produce over 480in-ozf torque and turn at a 60degree sweep in a .12sec transit time.
Let me warn you, these servos are not cheap. I think around $150-200USD for these (I do not know their exact current selling prices)

Some other high torque servos are Hitecs 5995, 5955, & 7955 servos, all producing 333in-ozf torque, and these gravitate around $100 each.