Not enough info
How many miles on your Expedition?
What condition is it in? Mainly the IRS pivot joints
Is the TV lifted?
Over sized tires? What is the PSI on the TV's four tires and what
is the sidewall max PSI?
Any other mod's to your TV?
The trailer weight you report is on the high side of any half ton, IMHO
Is the trailer tongue level at it's highest pointing? Better to be
slightly down.
What WD Hitch system are you using, what is the bar rating, head
tilt, etc
You also are guessing on way too many points that need actual numbers
Suggest you make a trip to local weigh station, garden supply, etc
that has a scale. Weigh the whole setup axle by axle and if they will
allow, with and without the WD Hitch tensioned and not.
Much more info needed before any of on the Internet can diag your issue(s)
