the scales are your friend
weigh your front and rear axles on a cat scale
or a dmv scale
in oregon we can weigh for free when the highway truck scales are closed
i have found that my new trucks and cars empty are hundreds (800) of punds heavier than the light weight shown in the owners manual
once you know your actual rear axle weight , that will tell you how much tongue weight you can use for your trailer .
for the best handling figure 13% tongue weight to get your trailer max weight .
for example if your rear axle truck weight is actually 2500 # and the gvw sticker of your pickup says max rear gvw is 3500# then you have 1000 # to work with.