I need your advice!!

It's true if Roadmaster says it is.
And it's also true that Roadmaster told you "no can do".

I don't think there are any lawyers who post here to answer your questions. If the best lawyer in the USA tells you he can git 'er done, he's probably correct. But I'm sure his legal fees won't come cheaply. Being betwixt a rock and a hard place doesn't leave you much choice though, does it?

If your lawyer CAN have your record cleaned up, I'd contact Roadmaster and ask them if his efforts will rectify the situation. It'd be a bummer if you spent big bucks to clear your record, only to be told no can do again.
If your lawyer can get ALL the blemishes off your record, I'd spend the extra money to have that done. Just be aware that although court records may be expunged, the arrest records will still probably be public record, and Roadmaster or a company you apply to for employment may be able to access those records.

If you fail to disclose that information to a potential employer it will probably be reason for them to throw your application in the circular file. And telling them up front could have the same results.

Alcohol and drug related offenses are BIG no-no's in the truckin' industry. That you have both on your record is going to be hard to overcome. The truckin' company's insurance carriers are often the one's pulling the strings, and the company's hands are tied as a result. Even if a recruiter tells you all is well, and sends you to orientation, don't be too surprised if they send you home after a couple of days. I've read of that happening MANY times.

At this point, if I were you, I'd forget about Big truck truckin' for awhile. It could trun out to be one big headache for you. But, if you're determined, hire that lawyer and see where that takes you, if you still have the funds to attend driving school after paying the lawyer. It'll probably cost about the same for both.
Is it worth it?