I live out in the country and drive mostly on gravel. What handles gravel better? A car or Suv or Truck? Does a higher wheel make a difference?

Truck. Diesel trucks have the greatest torque (hauling power). I'd go with a standard, full-size truck, preferably diesel. By itself, wheel height is not a major consideration.

Do you mean merely driving on a gravel road ? Or pulling or hauling a load of gravel ?

Trucks are best for driving on gravel roads--their suspensions are much stronger and hold up better. I would rank them in this order: truck, SUV, then car. Gravel roads are particularly brutal on cars.