engine size, transmission, rear axle ratio, & rim size are not the only things that are involved in the calculation
if you had leaf springs instead of coil springs, you could tow more
after all, what is the difference between the 1500 & 2500 series ?
here is a tow chart
click first on VEHICLE ( the weight shows when you click each vehicle,
then click LOAD WEIGHT, use the slider for heavier trailers
to see what difference wheel size makes, look at this website