I towed a 6000 dry weight travel trailer for years with my previous 2003 Expy 5.4/3.73 limited slip, 9200 lb tow capacity, in addition to my 6000 lb boat. It towed both OK. My typical speed on the interstate is 65mph. I lock out the overdrive on hills. You do know the 24 foot long trailer is back there, but no problem from a handling perspective. I would get 6mpg towing the TT and 8 mpg towing the boat.
Personally, I would upgrade the rad, in addition to the oil and trans cooler, as you indicated you do not have the HD tow package. I would limit the trailer to about 6000 lbs dry weight, to give you some headroom.
My new 2016 EcoBoost tows like a freight train. But I would not want to tow much more than 6000 lbs.
brick