Mileage on the vehicle may make a difference. Change the ATF often (and correctly-not all shops do. You need to get all old ATF out of the system and many shops don’t do it right. Sometimes only half.
The bigger the diameter of the tires on the trailer the better. Radials have less rolling resistance than bias. Keep tire pressure high. Balance the tires. They will last longer with less drag.
Aerodynamics of trailer also make a difference. Move air around the wheels like most tractor tire rigs with panels and suck in after the wheels.
Keep trailer as narrow as you can to keep it behind the tow vehicle.