Hi. Were your other liver enzymes normal?
Have you had a sonogram of your liver?
There's a possibility here that it was the alcohol that was raising your GGT and it might take as many as three months being alcohol-free for the level to return to normal.
Assuming the liver was normal on the scan and there was no evidence of a fatty liver (which can also elevate liver enzymes), I really see no reason for any further workup like a liver biopsy or a ct scan.
I think, for the most part, your liver is fine but you probably should abstain from all alcohol from now on