My TOS started out as RSI injuries and then spread into my neck , upper back and shoulders. {lots of repetitive assembly work, long hrs and fast paced - plus type A work ethic}

I had sharp cramps in the back of my hands at one point, then it was elbow pain, and then tight buzzing forearms, then the tingling and buzzing ring & little finger for a short time {I got my next batch of PT at that time}, then into the burning in the upper back and chronic tight and then finally spasmed neck & upper back muscles.

The forearm symptoms lasted the longest for me, but when I finally got advanced PT and chiro working on the neck muscles and upper back much of the forearm sx went away.

a rough time line for me -
RSI injury 1999 - recovery took about 1 yr
shoulder "strain" in 11/2002 - PT and light duty
shoulder & neck "strain" in 1/2003 - PT and lt duty again
All the previous injuries started gradually reappearing quite soon after I was released back to full duty work in 4/2003 and then lt duty til 10/2003
2004 off work and found a really advanced PT and chiro who knew enough to really be of help to me.
2005 was really when things improved a lot for me with arm use & stamina.

The best things that helped me -
Sharon Butlers stretches
top rib mobilization
self trigger point work with tennis ball, golf ball, finger what ever fit the best to put the pressure on the knots.
chiro visits - he does PT therapies too
far infrared heating pad
home electronic muscle stim { IF stim if you can get one}
posture work - laying over one of those large exercise balls or a foam cylinder {videos in our sticky thread} basically to let the shoulders drop back and down and chest open up is a very good one.
a rolled towel will work too, or just the floor with arms out if that's all you can start at. then progress as you can.

My stuff was mostly muscular and probably the sticky fascia that Sharon Butler talks about. And head forward postures.

Discomfort can cause increased bad posture.
The theory is -
In trying to relieve the pain you hunch or slouch - but that is the totally wrong thing to do as it stretches the already over stretched upper back muscles and shortens the ones in front of the body.
So your body starts to see this as the new normal, but it's not a good thing.