I have a 2001 F150 5.4L with a 3.55 deferential and factory tow package. I just returned from 500-mile trip towing a 22 ft Cabolt (3400 Lbs + Trailer + Gear) ~5,000 Lbs I’m guessing across the California High Desert. The trip included several long grades (Sea level to 5000+ ft in 100+ Deg temps. The majority of time I towed with O/D off, occasionally I had O/D on and the torque converter would unlock on smaller hills. The truck seemed to have plenty of power for the trip.

Now that I am home, I’m hoping someone can answer these questions for me:
First, how long can the transmission run with the torque converter unlocked in conditions described above before fluid temp becomes an issue. Second, while going over rough roads, it felt like the trailer was yanking the back end of the truck around. Can this be fixed / mitigated by switching to different shocks or LT type tires?

Thanks

 

In my opinion, you could tow that load in those conditions and not overheat the trans fluid. I pulled my 5500 lb travel trailer over some very hilly terrain in Arkansas and the only time I saw tranny temps (measured at converter outlet) over 200 was on a climb to Petit Jean State Park. I'm guessing 7 plus deg climb with a lot of switchbacks so speeds were in the 10 to 25 mph range. When I was at highway speed the temps were 160 to 180 with OD locked out. The amount of air flow through the aux cooler makes a difference.

I am considering load range D or E tires also. The rear sway bar made no noticeable difference and the RS9000 adjustable shocks helped some but "the tail is still wagging the dog". I have the usual weight distributing hitch setup with the friction anti-sway device.