Ford recommends a trany flush every 30,000 miles. With all the fittings. It is done in 20 minutes. Last place I took mine. Didn't have the correct fittings. SO, They dropped the pan, and changed all the filters for the same price as a flush. So I got NEW every thing at 60,000 miles
My F150's owners manual recommends transmission fluid and filter change at 150k miles, not 30k miles. Curious where you found that 30k recommendation. But 150k miles is hilarious. 30k miles seems extremely short though.
To the OP, I think with either 3.55 or 3.73 gears you'll be peachy. I've got 3.73 gears but my trailer is taller and heavier. I live in the hilly west and the truck does great. Did a two week trip through the Canadian Rockies last summer and it barely broke a sweat. We're heading out to Yellowstone for a week and a half tomorrow.
I am not sure if your transmission has the "auto downshift" when you brake in tow/haul mode, but I find that works great for getting down hills without using much brake. I generally put it in tow/haul, lock out 6th gear (again, not sure if your trans has that feature or not) and just let it ride. Enjoy the trip!
