I noticed one thing missing in what you've written--have you also had an MRI of the lumbrosacral spine? Given your weightlifting history, that would seem a logical place to investigate.

Weightlifting can, if not done properly and carefully, lead to problems in any part of the spine. I have a right side C6/C7 radiculopathy secondary to a weightlifting injury that involved a tear of the trapezius and rhomboids and a straightenin gof the cervical vertebrae--the neurological symptoms in my right hand began a few hour after the muscle injury.

With balance issues, it's often hard to tell if the effects are from muscular imbalance or from neurological compromise--you might also consider having nerve conduction studies done.

In any case, check out our Spinal Disorders forum:

http://neurotalk.psychcentral.com/forum22.html

--good expertise over there.