Dude,
It may also have to do with the extra weight on the axle. The equalizer bars on your hitch transfer some of the trailer's hitch weight to the front axle.
I kind of doubt that this is the reason, but it might be worth considering. I would guess that the change in geometry is more likely the reason.
Loren
------------------
2000 Quad Cab, 4x4, short bed, six-speed: U. S. Gear exhaust brake, MileMarker Select Drive viscous coupling, Velvet-Ride spring shackles, Painless Wiring circuit box, Optima yellow-top batteries, Super-Glide 5th wheel hitch, Reese folding ball gooseneck hitch, Drawtite front hitch receiver, Tekonsha Sentinel brake controller, Westin nerf bars, Clarion sound system
1995 Standard Cab, 4x4, long bed, automatic: Firestone Ride-Rite air springs, torque converter lock-up switch, 4" cat-back exhaust, Reese 20K 5th wheel hitch, Reese gooseneck hitch, Hayes Micro Control trailer brake controller, 100 gallon bed-mounted fuel tank with 12 volt electric pump & fill nozzle, Swiss Cap fiberglass cap