I don't know if you had time to look thru all {or many} of our useful sticky links -- http://neurotalk.psychcentral.com/showthread.php?t=84
first few links-
TOS info:first link has photos of position testing- down the page
http://www.nismat.org/ptcor/thoracic_outlet/
http://tos-syndrome.com/newpage12.htm
http://tos-syndrome.com
http://www.acofp.org/member_publications/thoracic.htm

there's good info in those and some will point you to other info on the sites so explore them fully not just the linked page.

If nothing has shown on testing {of a serious nature} a good thing you can start to do for your self is a home care program.

You can get some library books {videos are very good for this too} and study up on posture and whole body usage /alignment. { like Alexander, somatics, feldenkrais }
also a good and gentle stretching program will help until the docs get things figured out for you.
I really like Sharon Butlers book and website programs and info
{ www.selfcare4rsi.com }

the vertigo/dizziness was a big one for me - it could be vertebral artery sx from the c spine or from muscle spasms or sx from triggerpoints.
mine were from trp/spasms because after those got resolved the dizziness went away.

have you tried any good TOS PT /bodywork from expert therapists that seem to understand what they are doing?

Do you know how your pain & sx came about?
fall, car accident , repetitive injury/posture change over time?