How soon after he became a POW was his promotion and how high was he promoted. What grade of Sgt is he now? E-5, E-6 ????? Was there a time on grade assessment which led to promotion or was it just because he was POW?

Some news reports refer to him as staff sergeant, others just sergeant.

I think due to time in captivity he only got two rank increases, so that make him an E-5

From the US Army website:

POW personnel continue to be considered for promotion along with their contemporaries. Policy provides for each missing or captured officer/enlisted member to be considered for promotion to the next higher grade when they are eligible. The eligibility for officers is based on the date of rank in their current grade. For enlisted members, eligibility is based on time in grade and time in service.

Link to Army Regs

His promotion was based solely on time-in-grade

. . . the rest is history.