Normally I'm one to gripe about another new tire thread. The Google Search forced to search only the 5th Gen site works wonders. But given the 80+ hours I've spent in the last several months researching, sometimes a new thread with current information and easy answers is understandable. Hopefully the OP has done some searching too.
I'm not going to do more than to mention getting rid of the OEM dunflops is a good idea.
I ran KO2's in 275 E load for almost 22k mi, gave up on their wet weather performance and stiff ride. The ride was bad enough in the Ohio potholes that I will NEVER put another E load tire on my 4Runner.
For the last ~48k mi I've been running Cooper Discoverer AT3 in 275 C load. I've got nothing but good things to say about them, most of it already echoed in other threads here. I'm an occasionally aggressive driver, and they still have 6-7/32's of tread left. But come winter I'm going to wish for more tread in the snow.
My research has been over the past couple months with the intent to purchase during Labor Day sales. I've gone through lots of debates about size (that's what she said), and that really affects the available choice list.
Sizing
OEM 265/70R17, nothing wrong with the size, works great and lots of options especially since it fits the lower trims of the 17+ F150's. Has one option which really caught my eye, the exclusive to Discount Tire Goodyear UltraTerrain AT.
I really like the 275 size because it fits stock with no rubbing. However options are very limited. I looked into 275/65 and found even less.
I checked hours of threads on "pizza cutters" (255/80R17), but because of the sidewall height they're all E load. There was one post buried somewhere which mentioned never again running them and suggested a 285/70 instead in P or C load. Easier to replace, and the cut protection provided by E load just isn't worth getting beat to shit on a daily driver that spends 8-10 weekends at best off-road. I had not given more than a glance to the 255/75 size because I saw the same, however, after reading this thread found a couple C-load options. Although I've decided against narrow because of my fast cornering tendencies.
285, the most options outside of OEM sizing. Since I already have a lift/level installed, 285's are an option, though other mods may be required to get them to work.
To Consider
Your choices are likely different, but maybe some of what's below could be something to save someone else some time in research. Keep in mind, I've been looking for 275 or 285 /70R17 with an AT pattern, MT were not researched. Nor did I consider anything in OEM (265) sizing, though they are very likely available in all the tread patterns I've considered.
So the top picks on my short list are in no particular order:
Toyo Open Country AT III (3) - P285 or 285 C Load
Cooper Discoverer AT3 4S - P285
Falken Wildpeak AT3W - P285
Actually that's the whole list. It's short because there's so little in P or C at those sizes.
Other Considerations
I'm one of the horror stories about KO2's in the damp/drizzle conditions, so they aren't an option. I've heard lots of people with the Nitto's say similar things.
Cooper - all other Discoverer lines offer only E load.
Falken Wildpeak AT3W - 275 C, P285 or 285 C load. LT's have a massive 18/32" of tread, and hence are heavy in comparison to other tires of the same size. MPG would suck, and I wonder about balancing and treadwear with that much tire.
Firestone Destination AT2 only have 12/32" of tread in LT sizes. That's less than most P size tires! They are somewhat comparable in price, but starting with less tread for the same price is no way to buy tires. Destination XT is E load.
Michelin & Continental - Nothing larger than OEM for AT patterns
Dick Cepek, Mickey Thompson, Goodyear, Hankook - Only E Load options
Yokohoma Geolander AT - Had these on my mom's Outback, treadwear was horrible, they only lasted a year and <30kmi.
I hope this helps more than a few. I've gone cross-eyed on all this research, so I more than likely missed some options. We'll see who's got a better sale come Labor Day.