What effect will heavy use have on the life of our truck?

Will it shorten the life of suspension and drive-train parts...sure. There is no question about it. Exactly how much is much harder to determine as an individual and there is a good chance it will be a minor shortening (ie: if the engine dies at 230k miles vs 240k miles would you really be able to determine the exact cause?)

The issue is from your description, you aren't using the truck very often. Sitting unused is far harder on a vehicle than hard use (within ratings).