You'll like the 8.1 gasser with its big torque numbers down low in the rpm ranges.
Payload threads on a RV forum are always a hoot with all the guessing/opinions.
Always check with your state size and weight folks on how to find any trucks actual payload. I see your sig says Idaho .....
Idaho.....TITLE 49
MOTOR VEHICLES
CHAPTER 10
WEIGHT, SPEED AND TIRE REGULATIONS
(snip)
49-1001. Allowable gross loads.
(3) In determining the gross weight of a vehicle or the gross weight of any two (2) or more consecutive axles under subsection (1) or (2) or (9) of this section, the total gross weight of the vehicle or combination of vehicles or the gross weight of any two (2) or more consecutive axles shall be the sum of the axle weights.
For the purposes of this chapter the gross weight of a vehicle or the gross weight of any two (2) or more consecutive axles may be determined by accumulatively adding the separate weights of individual axles and tandem axles or groups of axles to determine gross weight.
49-1002. Allowable load per inch width of tire. (1) The maximum allowable load for any vehicle tire operated on any public highway shall not exceed six hundred (600) pounds per inch width of tire and shall not exceed the manufacturer’s load rating, whichever is less.
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The axle weights the code is talking about is not the "axle manufactures" numbers as roadside enforcement has no idea what they are or how to get that info. The axle weights are on each trucks certification placard which makes it simple for roadside leo to determine correct axle/tire and gross load for each vehicle.