lets beat a dead horse again..Tundra tongue weight max

In your case, your limitation is not payload, but the rated capacity of the factory installed, OEM Class IV receiver on your Tundra (of course, I'm assuming you have one). Typically, Toyota sets the maximum tongue weight capacity at 10% of the tow capacity, or approx. 1000-1050 lbs.---WITH the use of a properly adjusted weight distribution hitch. Without a WDH, it drops to approx. 500-550 lbs.