Like OC, I would check your shocks - how old is your 5th Wheel?
Chucking is typically caused by worn shocks and/or low pin weight.
Weight distribution is pretty important; best case is heavier in the front of the 5er. What you do NOT want is to have all your heavy stuff in the back (use your basement, that's what it is there for
On a totally different Vein You are a towing GOD!
I was stationed in the UK for over 4 years when I was in the Air Force and no way would I ever had the guts to yank a 8289 with a F250 down some of THOSE back roads
For those un-informed as to what I mean... Here is a photo of the A38 Country Lane 2 some Brits consider this a wide road
I suspect you are strictly a Motorway driver with that rig