It's not as much a problem getting started, it's getting that train to stop in a hurry. Tow limits are more about stopping and safe handling, than climbing hills etc. And YES I know that most trailers have brakes
as well, and some manufacturers address that and require those as well as a part of towing limits.
When you start out being over the rated limits you are opening a whole bag of safety related worms and, need I mention, many insurance companies don't think much of paying claims in accidents when the vehicle was being operated outside of manufacturers specifications. But you can always call yours and ask them what they think about the issue.
And, just recently a truck driver was sent to prison for manslaughter when his truck brakes
couldn't stop his truck on a down-grade in Pasadena, CA, resulting ithe death of a teen-age girl and severe injuries to her father.
However it wasn't because of the brakes
not being able to stop him that he was convicted, it was because he was driving an overloaded truck.....
Now some people will tell you about being a careful driver and everything will be OK and how they have been towing overweight for 35 years without problems and how the manufacturers towing limits are different in European or South American versions and how they are set low so you will buy a larger truck etc., etc.
It's like traffic laws, we break them every day, we take our chances and then we complain when we get a $550 ticket for a traffic camera violation. But, for the most part, they are there for good reason.
Like it or not, and the same should apply to tow limits.
And YES, this is my personal, rant and I approve of its contents