thanks for the reply flyboyike...sharing my reply on the Gwagen thread:
Thanks for your reply djdinaz, as you can imagine this issue has been driving me bananas over the last few days. Thing is, other than what was indicated in the vin decoder, I had no reason to suspect that my g55 was not genuine. And having owned several Mercedes AMG cars through the years I was fairly confident that I'd know how to spot a counterfeit.
In any case I think I'll take your advice and have my local dealer check both the car and VIN for me. Meantime, I think I've got reason to be hopeful after checking 2 other vin decoder sites:
VIN: ???????? VIN ??????????? Mercedes-Benz | CARInfo
Каталог запчастей Mercedes , подбор автозапчастей для Мерседес по автокаталогу.
While they still identify my truck as a G500 both sites indicate an engine code of 113.982 which is said to be the 5.5 liter AMG 354 PS as opposed to the g500's 113.962 5 litre engine.
Additionally also indicated in the SA Code is zy2 code which is said to mean 5.5l amg.
Based on some anecdotal info gathered from the various sources, early 1st gen g55s are often identified as g500s on VIN check - but with correct AMG engine codes as identifiers.
Also found this old thread from 2011 tackling the same:
In any case, keeping my fingers crossed.... thanks again!