<p style="text-align: left;">I work for several years for the federal government in several position, then I left the federal government and work for several government contractors. During that time I underwent a full background check which include a full poly with the federal government, the level of security clearance was TS/SCI/GAMMA. I am looking for a job with either the federal government of another government contractor, will it be difficult for me to get my clearance back</p>
It's been expired so long that they'll just do a full SSBI on you. Same as any other new hire requiring a clearance.
The difficulty lies in what issues may turn up since the last time you held a security clearance. If there are no issues then it will be relatively straightforward. With increased scrutiny on previously overlooked areas however, it depends on your application and the information within.