It took 4 trips to MEPS, even the MEPS 1st SGT knew my name there, and 2 recruiting stations, hell I even talked to a recruiter in Utah and I'm in California. I gave my recruiter 4 jobs I'd be willing to do (no particular order) 21M Firefighter, 35M HUMINT, 11X Option 40, 18X. Then I told him over and over again "I'm not gonna waste your time here, I'll join if I can get one of these jobs, and one of these jobs ONLY. I am not interested in anything else." Then I told that to the 1st SGT of my recruiter.
It'll take a lot patience on your part, a lot of determination and motivation (a lot like RIP). Your recruiter, and the Career Counselor especially at MEPS will tell you "no you can't have opt. 40, it's not open to PS (prior service) right now, but we do have this........" , which would be something you don't want like truck driver, or cook
This is what they offered me, I literally laughed out loud , then my laughing stopped for a moment when the counselor said he'd retired as a CSM 25 years in the Army 20 of them in the kitchen! 
Anyway that's probably true, it's probably NOT open to PS right now, key word there is "right now", because that doesn't mean it wont be open tomorrow. Everything at MEPS and I mean everything changes just about daily.
Now the major problem you'll run into is the counselors won't want to deal with you anymore. They want the kids that are joining right away, they'll straight up tell you to leave, they did to me twice, so you know what I did..........I left! Then I called my recruiter and he asks in a very fake excited voice "so did you join?" I replied with a chuckle "no, they offered me truck driver, cook, and some other crap" he says "so why didn't you take it" and that's why you need to tell your recruiter up front what you're willing to take and nothing else, so I was able to respond with " I told you from the beginning what I'm willing to do".
Then he got TOP on the line and I was able to tell him the same thing. Now my 1st SGT was a stud when it came to wheeling and dealing, if anyone is in the Los Angeles, or Orange County area PM me and I can put you in contact with them.
That was the 1st time I went to MEPS, the next time I went it was the same 'ol story with the counselor, then the 1st SGT gets on the phone and I tell him " you know what I'm willing to do so......." then I had a thought so I strategically gave TOP the jobs I wanted in a particular order this time 21M, because I knew there was no way, 35M and 11X opt.40 either or I said , because it really was a toss up then 18X last, because I figured they'll try to give me something other than my LAST choice.
I've come to notice usually the Army gives you your second pick, so make that your real first pick. SO MEPS says cook and some other stuff, and TOP says 68W Option 40 !!!! I just heard option 40. But I don't want to be a 68W so I told him " you're almost there TOP, just make it 11X", but I knew then it was possible. I ended up leaving again.
So fast forward 2 more times and today's the day!! I have the counselor sitting in front of me, my recruiter standing next to me on the phone with his 1st SGT. The counselor says "what do you want" I gave that same order of jobs, she gets on the phone................ low and behold she circles 11X OPTION 40 !!!! She was the 4th counselor I'd spoken to in this 2 month period.
I had everyone and i mean everyone pissed at by this time. TOP had told me the day before if I didn't pick something, anything cook, driver, stripper whatever
he wasn't gonna deal with me anymore, last chance he said. She (the counselor) hung up the phone and told me that that was the only job I was able to pick that day! There weren't other options for me. Now I don't know if it was the 1st SGT who did something I tend to think so, I didn't ask, I didn't care. The other counselors even came around and said they'd not seen that happen in a very long time, a few even said they'd never seen it. So moral of the story, it's your life you're dealing with you're the one that has to do the job when you ship, they get to stay there and keep treating prior service soldiers like second class citizens, but you still have to do your job. So be selfish, don't be flexible you wont be doing the Army or yourself any good stuck in a job you don't want.
This whole ordeal took many times a week every week of arguing being called names, visiting the recruiting office, meeting with the 1st SGT, phone calls, my cell phone bill was HUGE !!!! But if that's what it takes then Drive on !!!!!!
