Possible after 5yrs on vicodin 5/325 to occasionally still get weak/tired/sob etc? i take half tab q 2 1/2 hr instead of q 4-6hr. i do have mg also.

Yes it is possible: If you are taking 1/2 (2.5 mg) q 2.5 hrs around the clock or even 12 -14 hrs a day for any length of time you could be showing signs of opioid dependance, albeit at its early stages. At some point you went from q 4 hrs to q 2.5 hrs, likely due to your becoming tolerant and need a higher dose. Early withdrawal sx include fatigue, weakness increased pain and/or anxiety or depression.