I towed exactly the same size trailer a new forum member is planning on hauling. Mine was an enclosed box u-haul trailer. This was the height of the trailer loaded up. Note the height difference between the two. I had ordered a 4X8 enclosed, but upon picking it up, I found the tires were ten years old. Having an idea that I didn't want to wait for tire repair service, I opted out of this smaller trailer and was upgraded to the 5X8 for no fee. However, having a shorter-roofed trailer, to me, was a better choice, but was not going to be an option at the pickup site.
Now, I drove about 65-70 mph as much of the move as possible. Considering I have the 4 cylinder engine, I was going about 27 mph over the Appalachian Mountains around eastern West Virginia.
It doesn't look steep, but it certainly was for 3/4 of a ton (1,500 pounds) of weight and knowing I could tow 3,500 pounds.
My transmission temperature got up about 235 degrees on the temp. gauge, but it never went higher than that.
I do not have the pusher-style fan installed on the front of the cooler...yet.
Advice: My wife had the bright idea of becoming members of and staying at KOA's (Kampgrounds of America) along the way since we are a family of 6 (kids and dogs). Every night we stayed at a different KOA. The stops we made from the
two cars we drove were the KOA's, gas stops, potty breaks for people and pets, and only one for the radiator (cooling system) almost over heating through the badlands of South Dakota.
Zoikes, Scooby!!
Okay, maybe it did overheat, but it was still drive-able after a little stop.
I don't know, to this day, why it did this. Maybe the radiator needs to be replaced, but after adding more undiluted Toyota-specific coolant to the radiator at the Rapid City South Dakota KOA (Mt. Rushmore tourist site), it seemed to work just fine after that. It no longer, and has not since, overheated.
Trying to find a place for the pooches 'Roonie and Sophie' to play was tricky. I had them, the wife had the kids. I got lucky on this move.
'Roonie's' play face.
http://www.youtube.com/watch?v=vWrrNCVOhII
Mild car wreck:
http://www.youtube.com/watch?v=NA1-wHTZ6Iw&list=UUj0Yn6aGTqayWo4clGFnxqw