Addressing the issue of your fifth wheel taking weight off the front axle, inspect the position of the hitch in relation to the rear axle center.
The hitch sounds to be too far back, slightly behind the axle, instead of in front of it, to be removing weight from the front axle. Maybe something is installed wrong, backwards, or adjusted to the rear. Is it a sliding hitch?
The fifth wheel should add a slight amount of weight to the front axle, with the hitch mounted such that the kingpin is a few inches (about 3 to 6 inches) ahead of the rear axle centerline.
