How far does companies look back into my record

I am trying to get a better job in Louisiana with my cdl but I don't know if any one will hire me with a dwi that I got in my personal vehicle 4 years ago.

I heard from my boss that he can put me on his insurance after 5 years but I am getting older and it is hard work looking for something better.

So far I haven't been able to find any answers to my ?'s I just want to know how far back do most company's look on my record for employment reasons.