I'm using the GI Bill, so I've got a little bit of information, but I've only done the bare minimum of research, so keep that in mind.
The first thing to know is that the GI Bill isn't going to pay for all of your schooling. The amount they give you is based on the amount of time you spend at the school. Most trucking schools are 4 weeks, so you'll only get whatever GI Bill pays for 1 month. I believe it's somewhere around $1,000. Yep, less than the $1,200 you paid into it. Ain't that a kick in the teeth?
Be sure to contact the person in charge of funding at the school you're interested in, and tell them you want to use the GI Bill. I don't think all schools are automatically eligible to use it. Ask them what their Facility Code is.
http://www.gibill.va.gov/
Go to the GI Bill website, download and fill out a Form 22-1990 once you've decided on a school. Send it to the VA, and they'll have the school send them another form. You'll get your money only after you graduate, but you should start your paperwork before then.