Hi there Tassiedude

I thought I would add my 2cents worth.

I have an 04 F250 XLT dual cab. The first owner removed the style side and made a very heavy solid steel tray for it.
The weight of the empty vehicle with fuel tank full and me sitting in the drivers seat is approx 3700kg. My GVM is 4217 kgs (actual front axle weight is 2100, rear axle is 1600), so this only gives me a payload of approx 500 kgs.

Yes the rear axle rating is 2760 kgs, but you can never use this rating because you will reach your GVM way before the rear axle reaches it limit.
IMHO, the rear axle rating is only used when towing a gooseneck/5th wheeler trailer as you can put approx 1000 kgs on the ball. Your vehicle GVM is not used then, the Transport guys use the Combined GVM which from memory is approx 9000 kgs.
I approached a vehicle engineer in Brisbane, I explained my situation and showed him some figures. He said he would increase my GVM to 4495 kgs if I added some airbags to the rear springs. I could possibly go higher, but I would prefer not to as once I pass 4500 kg GVM, then my rego almost doubles in price.

So at the moment, I am getting a new alloy tray made, which will hopefully cut my weight down abit and with the higher GVM, I might just get a 1000 kg payload rather than the 500 kg I currently have.

On a separate note, I bought mine as an auto as Ford only imported auto dual cabs. I then converted it to a manual ZF6 box and also a manual transfer case. This has improved the driveability of my F250 ten fold as I prefer manuals.

I hope this helps.