Hi,
Game Theory is very broad and widely used in Operations Management (OM) /Decision Science (DS), Marketing, Finance and in a host of other areas. So firstly, you have to select an area of interest. I would suggest you to read research papers and see what excites you the most and then find out professors who work on similar topics in your target schools. If you want to delve into the theoretical side of game theory you can perhaps start by looking at DS programs.
Secondly, the degree from IIMA would help you but you need to have a good reason for wanting to shift to academia after 5 years - perhaps some aspect of your work interested you and you want to research on that? A lot of people in OM/DS and Marketing have engineering undergrads so that is perfectly fine. Your GPA 5 years ago should not matter a lot as long as you do well in GRE/GMAT - but maybe others can weigh in on that.
Hope that helps!