<<You are a wuss! You are not an experienced driver. You will fall asleep at the wheel. I drive a 91 Toyota PU now with 200K miles I control everything. Driving long distances is a skill and craft.>>
I really hope you are joking in the first two sentences.  Wanting and using cruise control over a 5 hour constant speed trip has nothing at all to do with being a good driver.  In fact, I have found that I am more alert when I use cruise control in that type of situation because otherwise my foot gets very tired and I end up concentrating on that, which is not good as my concentration should be on the road.  There is no evidence that he will fall asleep at the wheel.  I have driven several thousand miles on the interstates using cruise control and I have never once had a passenger become worried about his or her safety on such trips.  While I will agree that cruise control is not a necessity and that it should only be used on expressways with minimal traffic, I have to say that there is no good reason for such prejudice against cruise control.  Back on topic, Dismal, while I'm sure that it will be some way to put cruise control on the truck, but I would not be surprised if you were to find that it will cost more than it is worth.  Still, good luck, and don't pay attention to people who say that cruise control causes accidents.  As long as you remain aware of your surroundings you will be fine.
Zenmervolt