What they said^
You may not be able to keep up with the left-lane traffic, but you'll make it.
The Triton motors can run at high RPMs indefinitely, and it doesn't hurt anything besides gas mileage. Pulling the Siskiyou grade and the grapevine with 15,000 pounds in tow means even my V10 is in 2nd gear, staying around 5,000 RPM for 10-15 minutes at a time.
My only other note: If you have lights in front of the grill, make sure you monitor transmission temp. Stock cooling is fine, until you block the airflow. After adding my lights I had to up-size the transmission cooler.
Oh, and make sure the rear-diff has synthetic lube. It comes that way from the factory, but quick-lube places try to talk my into conventional every time I go to one