Old thread, too late to affect the O/P's decision, but it may help others.
I don't believe it is "necessary" to lift the trailer and in any case doing so would make it less stable.
REMEMBER horse and livestock trailers haul live weight, i.e. the mass moves around.
I would;
a) set it up to clear the truck, accept that it has an "up hill" attitude.
b) get it weighed axle by axle, if the tires are within their load range WHEN THE TRAILER IS LOADED leave it at that.
You may be surprised at just how close the axle loads are to each other.
This is based largely on the assumption that tandem axle equalizers (noun) DO in fact equalize (verb) the load bearing to the axles.
Torsion spring axles also equalize quite well.
As to how it looks; don't worry about THAT

As to how it affects the horses; Assuming you accelerate gently braking forces are likely to be worse than accelerating forces, so a slight up hill is in their favor.
Also, getting pitched forward from braking is harder on them than getting the push from behind - again a slight uphill relieves this.