Not sure what the "25% weight distribution" is. It's not a commonly used term.
Something is still off with your numbers. If you connect the trailer without the WDH hooked up how is the truck weight not increasing at all?
- Truck only 9,760
- Truck with no WD, 9,760
I'm guessing the trailer is somewhere around 9000lb, so it should be adding somewhere around 1000lb to the total weight of the truck due to hitch weight being added.
Also, how are you measuring trailer axles when weighing the truck only? This does make sense and even if you did unhook on the scales (not something the truck stop is likely to want you doing), the trailer axles should be identical (or pretty darn close) to the trailer hooked up without the WD. You would also need to define which pad the trailer jack is sitting on (if it's on the same one as the truck, it's going to get added to your truck rear axle measurement).
As far as sway, define what you mean:
- A passing semi's bow wave will give the rear a push but as soon as they are past, it should settle right back in line. This is perfectly normal. If you are going 55 and the truck goes by doing 85, it can be a pretty good push but as soon as he's past, it should settle down.
- Sway is when something gets the rear swinging back and forth and the semi is long past and you are still swinging back and forth. This is a problem because if you make a mistake dealing with it, you can lose control.