Our 14,000 lb. fifth wheel was right at the weight limit of what our 2007 Dodge 3500 could tow, and the pin weight of the trailer along with all the things we carry in our truck loaded down the bed of that truck quite a bit.
When hitched up, although the rig looked quite level, the truck sagged a bit, leaving the front wheels a little light and giving the truck a tendency to wander.
To alleviate this, we installed a Timbren Suspension Enhancement System between the axles and leaf springs of the truck. These are solid rubber donuts (not airbags) that fit between the axle and the leaf springs. That made the truck sit better and wander less.
We had that setup for eight years. In 2016 we purchased a 2016 Dodge Ram 3500 dually truck which had a much higher weight capacity in the truck bed and could handle the pin weight of the trailer along with the additional weight of the water jugs and leveling boards we carry in the bed of the truck much better.