I'll agree with mowermech and wing_zealot.
Add#4
Know what the performance specs of the manufacture really mean. example, the new towing specs only requires a rig to go up or down a 12% grade, 13% if it stalls out, its made spec! I've been up and down locally here in the greater Seattle Puget sound region local roads, driveways in the 25-35% range. I've also stalled out many a rig do to NOT HAVING the correct drivetrain to do the task I need to do. Yet I was under the manufactures generic rating. Blown a transmission or three too! So make sure you understand what the ratings actually stand for, before you go over or under the ratings and assume you will be ok.
Like Mowermech, I have pulled both over and under ratings, been safe above, unsafe below due to a poorly loaded trailer and it swayed uncontrollably. As one causes an accident....."BUT OFFICER, I was under the ratings, so I must have been safe!" A rule in Wa st, if a trailer movers more than 12" off center, your are unsafe, get a ticket, and have to fix the problem before you can continue going down the road!
There are a number of other rules, codes and laws similar to this. Same as the legal weight you go down the road. My C2500 has an 8000 lb plate on it, at 8001 lbs to door sticker of 8600, I am overweight! Door sticker number means squat here! Manufacture gcwr number is not a legal number from a enforcement number either. You need enugh paid for tag including the truck and trailer to be legal per say. IE pay the tax for the damage to the roads you are doing at a given gvw. Looke up federal bridge laws to see what your true max legal weight is per axel, what can limit it etc.
Marty