It depends on the size of the truck. If he is in a standard "pickup" truck, we would say:
>> The driver got out of his truck.
If it is a large "big-rig" or tractor-trailer, where the driver's seat is high above the road, we could definitely say:
>> The driver got down from his truck.
>> The driver got off his truck. [ ... NOT "off from" ]
Your example sentence is OK if the truck is a very big one:
>> The driver got off his truck to help me.