Thanks very much for the replies. I think you're right, it's probably not possible to know for sure.
My truck is a 2011 Toyota Tacoma (4x4 double cab). It does have built-in electronic sway control. I do not know the actual tongue weight of the trailer. The manufacturer says the dry hitch weight is 445 lbs. I asked, but the dealer couldn't tell me the actual weight. I am kicking myself for not being better prepared when I went out to look at it.
Anyway, I just borrowed my neighbor's utility trailer, and loaded it so the tongue weight was around 550 lbs (I have a Sherline scale), and the truck was lowered just a hair over 2" at the hitch, and about 1.75" measured at the rear wheel well.
