That'd be a long reach from the hitch (normally located at the ack of a truck) to the hood.
Go to a home improvement store and dpick up one of those 20" tall planks / steps that is aluminum, about 30" long and folds up. You'll have to have a way to reach the top of the cab anyway. I can reach the whole hood w/o leaning on the truck (Ridgeline), but the middle of the windshield and the cab are no-go's w/o the plank. I have to move it twice on each side to reach the entire area. They also make a great platform to lay down your PC when polishing.
Here's a previous thread on washing tall vehicles.
When it's too tall...