AWWWW Yeaaaa! one of my favorite subjects!
Disclaimer: I'm not going to reference sources. This is from growing up and working in one off, ground up build shops, and learning from guys that were racing cars from the '30 and on.
Everything that guy said was right, with just tire size. That was fine even 15 years ago, when overdrives were still around .79:1, aerodynamics weren't that big of a deal with manufactures. Vehicles from the factory had a lot of aerodynamic drag, and fuel prices didn't matter so much. You could take any V8 truck, lift it 6 inches, mud tires, and you might of been ok if living in florida on flat ground with lots of air. So when those era of guys regeared the factory ratio, to a ratio only for a bigger tire, they didn't have to account for the aerodynamic loss, or a transmission that can drop into a second or even third overdrive gear.
Now for a modern, 200 series, tacoma, 4runner, silverado, F-150 (you get the point). These manufactures are spending significant time and money on decreasing the drag coefficient. From the 3rd gen Tacoma with ways to let the air not stick to the sides and release freely off the back, to domestic trucks with as much air dams to not the air get under the truck as possible. Manufactures are then gearing vehicle for their aerodynamics, not the few people who lift, and even take aerodynamic feature off. So the trucks themselves are geared higher (a numerically lower ratio) in every effort to gain every bit of available fuel economy. It makes sense, it just needs to be taken into account if you modify.
Before talking about modifying look at just the 200 6 speed vs 8 speed.
6 speed had a top gear of .588 with a gear ratio of 3.90
8 speed has a top gear of .672 with a gear ratio of 3.30
The power output didn't change, and now you are gearing the whole truck to to maybe get a bit better of fuel economy, it didn't work as the EPA specs are the same, it was really done because of marketing that is (all other 2016 200 series still have the 6 speed) but that leaves you with more against the truck when you modify.
Now for modifying.
Adding a bit bigger tire will change things, absolutely, but the real issue is on the highway and wind resistance. Lifting creates more drag from wind getting caught, then taking the aerodynamic front bumper off and replacing with a winch bar that lets wind now get caught in the wheel well area, then increase rotating mass and weight from the larger tire, all have more effect on todays trucks than the truck of 15 years ago that already from the factory were geared to deal with no aerodynamics and were aided by lower ratios because we didn't care as much about fuel economy.
My '11 200 got a strait up 19mpg at 77 mph highway, all day. Hills and wind didn't require the trans is unlock the torque converter or drop a gear. Even a big 200 can still cut through the wind. When a front ARB winch bar was added and a normal 2-3" lift (still stock tires). I got a solid 16mpg, I couldn't stay locked in 6th on sight uphills. Add 295/70r17 mud tires... 11mpg and 6th gear was non existent. The low RPMs and massive increase of drag that a lifted, winch bumper, mud tired, and RRT'ed 200 just needs more power than what 1600 rpm can deliver.
If I would of regeared for just tire, I would be at about a 4.30, but that didn't take into account aerodynamic drag increase. So I went with 4.88. and I am now at 13mpg. It doesn't over rev, the transmission still requires a downshift on steeper hills. But I can generally get on the highway, on flat ground a cruise. So that when I'm loaded down with camping gear, driving up a Wyoming mountain, with a 40 mph head wind, I still have to drop gear or maybe go to 4th, but I won't have the issue that the guy who just compensates for tire size has when he has to drop to 3rd. And I've been that guy in the past.
