At first you should tell us your plan clearly!!

How long are u gonna stay in US?
Do you wanna get MBA?If u want,u dont need TOEIC.TOEIC is only for Japanese company.
Are u gonna get job in Japan after you leave US?

I just thought what u say is contradiction.
You`d been working at UK company in Japan right?
I think you`ve already got TOEIC or your job didn`t need english?