As I understand the years, the G55 has never had the 7 spd transmission found in the GL. The 550 G 2009-2012 did though.
The G55 2005-last year of it, 2011, had the 5 spd.
With 2012, they both (G550 and G63) went to 7 spd but they are not the same either, the AMG gets the "speed shift plus"...