towing with older 2v 5.4 triton

We towed extensively (6500 lb. loaded) with our 2004 Expedition with the 5.4 2v. As I remember it has peak torque of 350 @2500 RPM. The 3v version increased torque to 365 but moved the peak uphill to something in the 3400 – 3600 RPM area—I’ve read that the torque at 2500 actually decreased. We have a 4R75 transmission but I’m guessing OP has a 4R100 (E4OD). I’ve heard of a high percentage of folks with failures on that transmission just over 100K mi. (including my son and 2 of his friends). The older Ford 4 speed auto trans tend to open the torque converter a lot in OD to get more torque on a hill. This generates heat, the enemy of transmissions. When the Expy was new, I experimented with OD on and off and noticed no difference in fuel mileage. Since there is no fuel savings I mostly ran with the trans locked out of OD to extend the life of the transmission which is going strong at over 100K mi. Locking out OD also gets the RPMs up toward peak torque. I think OP will be just fine but there will be mountains at 3500 RPM in 2nd gear.