It doesn't sound to me like you have a big interest in big trucks. i will tell you though, that working on them is a lot of adventure, and less aggravation. The mechanical parts are almost all universal. As in, you could pull a motor from a Freightliner,and bolt it into a Pete in a few short hours. The parts are made by outside companies. You can literally buy, any truck / engine / tranny / gears / suspension, or any kind of combo you want. This is great for your learning curve. If you learn Detroit diesels, you can work at any make, dealership, or repair facility, etc. I could go on all day about mix matching.
The point is that getting parts, learning to work on them, and their systems, and everything involved in them is much easier to learn, better paying, and in most cases, more rewarding. A job at a freightliner dealer or a Paccar dealer (Peterbilt/Kenworth) would be great for you. I've got a monster fleet of my own. Mostly all Freightliners. They look great, run supebly, and are generally a very reliable piece of equiptment. Try a truck dealer. You'll be amazed at what your looking at, and the size of some of the parts, etc. I've got a lot more, but don't want to kill this thread. If you are interested we can talk about it. I can give you advice, and great suggestions. I've been in the business forever, and have a lot of contacts also. I can help if you'd like. Get me in a p.m., or email.