I think if your pulling a trailer that’s 10’000 plus in dry weight adding fluid or weight by any other means would have very little effect on way or the other.
The fact that a “tune” on my truck dramatically started the chucking and a tweaking of the tune made it go away makes me suspicious that the “drive by wire” technology in modern trucks may contribute to chucking.
I pulled lots with carb vehicles and never heard of or experienced chucking.
When my truck was chucking it would do it on everyone of my 3 trailers. 34 foot Cedar Creek with trailair, 28 foot goose cargo with 7 K axels and a 28 foot goose flat deck.
The key info here is that I could make it start, and stop, chucking with just The slightest pressure or lack of, on the pedal. Almost indiscernible. But it was this fact that made me ask the tuner,EFI Live, to Try some changes. They did
It worked. My truck never chucks.
Now this is my conclusion. Because of the modern technology that controls the accelerators in modern trucks I believe a stock truck may well chuck. Factory settings may well not take into account towing dynamics that can vary widely.
It may be possible that we can not feel our foot slightly pulsing on the pedal when the truck starts chucking but no doubt the truck picks up the signal and we contribute to the motion without realizing it.
Just my thoughts.