Hi
One of the reasons that it pulls hard may be the tire size.
It looks like 15" rubber by the pic. Make sure you have the tires at max pressure and see if that makes a difference.
I have a car hauler with 16" rubber,my buddies trailer is built lighter with 15" rubber and it pulls harder loaded.
Rolling resistance of a smaller tire that has a bigger contact patch because of lower air pressure.
Thomas
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews