Lay it diagonally down in your P/U. Then put a weighted down tarp over it. I use a net over the top to keep the tarp from flapping. Sometimes I use a coiled up hose to hold the tarp down.
No reason to stand the tree up and expose it to the wind.
Mike

mike is right. Lay it down and cover it.

By all means, bundle the tree with a tarp or heavy plastic tied very securely around it and lay it down to keep it out of the airstream as much as possible. If left uncovered, not only will the leaves be stripped off but the branches will be thrashed. I'd also find a way to hold the soil in the container tightly; otherwise while its on its side much of the soil mix may fall out and the roots may dry out. If any branches rest on the truck, pad them against chafing. Most JMs of that size are fairly valuable.

This post was edited by dwpc on Fri, Nov 15, 13 at 10:53

I only had room to lay it on its side at about a 30ú angle from horizontal, with the top of the tree pointing towards the rear. I was concerned that a tarp flapping in the wind would cause more damage than with it off so I made the trip without a tarp. I tied some padding around the soil to hold it in. There were still a few leaves on the tree when I arrived and I saw no evidence of any damage to the tips of the branches. My speed was no faster than 55 mph and probably averaged about 45. I can only hope that there is no unseen damage but I should know in the spring if there was. Thanks for your opinion everyone.

This late in the season, even though there were some leaves left on the tree, I believe everything will be alright. They were going to fall off in a short time anyway.
I have transported thousands of trees in pickups at all times of the year in over 35 years as a landscape contractor. My advice was a little more than an opinion.
Mike ;-)

I was out looking at my maple today and the new buds are just starting to grow. I didn't see anything that looked abnormal. So three months after the move and replanting, everything is looking good.

Thanks for the update.
Much appreciated.
Mike