hi all , im new on this site , i just bought my son a 1/18 nylint jeep and noticed and not sure if its running right , when climbing over obstacles the front end has power to pull up and when the rear tires make contact ( eg going over a tree root or paving slab )the wheels stop moving and car seems to rely on the front wheels to pull it up and over , the car is brand new and not sure if ther is a fault with it , any advice would be greatly appreciated , regards, daniel