No, the manual and automatic versions of the Crewman are rated to tow up to 1600kg and 2500kg respectively with a braked trailer. This is to protect the clutch of the manual versions which could easily be damaged trying to tow the automatic's 2500kg.

It's generally accepted that the more progressive take-up from rest of an automatic transmission makes it the better solution for a tow-car in the first place. And that extends beyond any single make or model.

Have the diff mounts checked; they're likely to be the cause.

I would approach Holden with a claim for part compensation, the only to do it is through your dealer in the first instance, and then direct to Holden of the dealer rejects you. If you do choose to make a claim against Holden have all your documentation available to give to them, and that includes the car’s service history. You also need to be able to support your claim that you haven’t abused the transmission. If they did agree to your claim, and I doubt they would, they would most likely supply the parts to rebuild it, and leave you to pick up the tab for the labour.