Sponsorships really can be touchy. It depends what you're plan is for it. In my case, it's a show truck, vs a Cummins drag truck, so the type of parts are different. I've found that your build has to be something different, and unique. In my case...that's part of the reason why I went with the ostrich interior, who the hell does ostrich in a lifted truck?
You'll want to also get a some professional pictures that you can use to market the truck. It sounds stupid to say, but you have to be kind of a sell out to a point. Make a Facebook page with build updates, pictures, any shows or events you're going to etc. Also, it helps to have a dedicated email account.
Then, write up a form letter. From there, email the fwak out of companies till you get responses. You'll want to present yourself in a professional way, that sells yourself, your truck, and also benefits the company.