Most states require a trailer with brakes and a brake controller above around 3000 lbs. A little different state by state, but the 3000 lb is a good rule of thumb.

 

 

I will bet that you do not have a trailer tow package. the newer F150's come with a reciver. Go to a Ford dealer with your vin# and ask them to print you a copy of the factory swindow sticker. If you got a tow package it will have a trans cooler and most will have the brake controller. The "max tow" will have a bigger cooler, radiator heavier rate springs and swaybar and brake controller, if you have a 2017 or newer it will also have 18" wheels. For some reason the 2018 have to get 20" wheels for the max tow. Also you don't need max tow for an 8,000 lb trailer. It won't hurt anything but not needed.

 

 

 

 

 

 

On my recent long distance tow (2850 miles) with my travel trailer, I noticed that my 2018 3.5L with the 3.55 gears will hold 8th gear at 63 mph turning approx 2100 rpm in tow/haul mode. If you let it climb to 65 mph, it will allow it to shift in to 9th and turn ~1800 rpm. That 8 to 9 shift is entirely speed dependent. Even on completely flat ground, if you let the speed drop to 63, the truck automatically drops that gear and will not shift back up until you reach 65. I tried it both with the cruise on and off and it will not hold 9th once you drop to 63. I've noted .6 mpg increase mileage letting it run a little faster in 9th as compared to holding 8th (11.2 vs. 10.6) while towing. I've always pulled my trailer at 62-63 but this truck really likes that extra few mph with these gears.

I'm not sure if the 3.73's will act the same or if it will move that 8-9 shift to a lower mph and move that max efficiency point lower. Maybe someone will chime in that has some experience with the 3.73's. The speed that you like to tow may factor in on your decision on the gear set.

 

 

It may have trailer tow but it doesn't have Max tow with 3.31 gears! For 2018 with the new 10 speed it calls for 3.55. Earlier years called for 3.73 gears.

 

Your 2015 Truck didn't come with a Trans Oil Cooler it must be a Add on check it out good to make sure the Lines were installed properly
you don't want to have the lines to blow when you are towing!!