Holden rodeo towing capacity

Hello,
I have posted this thread in caravanners and rodeo forum but am not able to get an answer also spoke to holden dealer who know where I am coming from but cannot answer.
I have a query regarding the towing capacity of my 10/04 plated RA model diesel rodeo.
The towing capacity is rated at 2000kg which is fine but the owners handbook has a GCM of 3750kg. When I purchased the car which was in 2005 I was given a brochure which is dated January 2005 which shows a GCM of 4900kg. I have spoken to holden customer service (who are non technical) who looked up the owners handbook and inform me that the owners handbook was not revised until November 2005 to reflect the revised GCM. What they could not tell me was the legality of exceeding 3750kg GCM or even what was changed in the vehicle if anything to allow such a massive revision of the GCM. I have spoken to a retired Holden engineer who is of the opinion that the GCM was revised in answer to competition with other makes and not due to mechanical changes to the vehicle between 04 and 05. I am close to the 3750 GCM limit with a new van purchase and do not want to have to watch every kilo I am loading in vehicle and van so as not to exceed it.
Hayman Reese and holden both sell a 2500kg hitch for the rodeo and hayman reese tell me that holden revised the towing capacity across the range retrospectively but to go to holden for the revision. The dealer says I know where you are coming from but go back to holden customer assistance as we do not know.
Thanks.