It is not a GT. When I saw the top part of the frame when scrolling the pic, I thought Redline or Haro. I see that there is some form of Haro decal on the bike so that is likely the case. That was a relatively popular frame style in the late 80's and early 90's.
Jeff Archer
First Flight Bicycles
216 S. Center St.
Statesville, NC 28677
704.878.9683
jeff@firstflightbikes.com
www.firstflightbikes.com
Always looking for vintage mountain bikes/parts/literature
so that's what he sent-maybe REDLINE?