I have a Lance 9'6" TC on my dually and my rear axle weight is 6000 even, loaded and ready for the hills(No trailer)...By the picture you posted,the ATV is mostly in front of the axle on the trailer putting most of the ATV weight on the truck rear axle..
I haven't weighed with the ATV trailer but because of the hitch extension,I am aware of the tongue weight of the trailer when loading.
Might try moving the ATV farther back on the trailer to lighten up the rear axle/tire weight..
Trailers behind a huge TC can really increase the rear axle weight of the truck and pressure on the rear tires...Tongue weight is everything in doing so...
Nice rig..I sure like my older Lance..Trouble free just like the other two Lances I have owned..