RC, you can get it re calibrated by someone like Sgesco in Brisbane.
I've got a customer in Atherton with a heap of Fuso's who had exactly the same dilemma and that's just what he did.
Everything over 12,000 kg GVM has to be speed limited.
I have been driving a couple of company new hinos ( supposedly 280hp) ... For some reason my heavier 250hp cummins Acco is a lot faster on hills ... Can the 280hp be a lie ? Or just measured from midget horses ?