The 4-Runner drive train really is obsolete technology. Toyota has great components to place in the 4-Runner, but has elected not to give the 4-runner customers the best they have to offer. They could easily drop the Lexus GX 460 drive train into the 4-runner and probably get close to the same gas milage or maybe better. The GX 460 gets 20MPG on the highway and is significantly heavier. In my opinion, Toyota knows that 4-runner customers have few choices, so they will only make minor changes to maximize their profits. Yes, I am very disappointed with Toyota for not giving us the best technology in the 4-runner, but I have owned many 4-runners with my choice is driven by reliability, not performance factors. If the Jeep reliability goes up, we may soon have a little competition, since the performance factor are really better in the grand Cheroke except for proven reliability.
1) weight has very little to do with highway fuel economy. Aerodynamics and torque around 2k RPM (and thus the ability to stretch out the gearing) have more impact on fuel economy... especially on the EPA test. The 4Runner would likely get 20mpg highway despite lower weight. Weight impacts rolling resistance drag which is not much compared to aero drag at highway speeds. Weight does kill your city mileage.
2) The 1GR is every bit as advanced as a Coyote 5.0 or the Jeep Pentastar. Dual VVT, roller rocker valve train, light weight oil, etc. The only thing we lack is ratios in the gearbox.
3) if you checked out consumer reports, the 4Runner is as fast as an Ecoboost F150, as fast as the JGC V8 (pre 8 speed), faster than the JGC V6 (pre 8 speed), and just as efficient. On the specsheet, the 4Runner is outclassed; in reality, it all works together very well. If you want to buy based on a spec sheet rather than what is the best on the street and off the pavement, by all means, that is your choice. I'm interested to see the new numbers for the Jeep via Consumer Reports rather than the easily gamed EPA tests.
4) Every engineering decision is a compromise. The 4Runner, being Japan built, has to do what they can to keep the cost down. They aren't being built by UAW newbies for $15/hr and parts sourced from Mexico. Given $xxxxx to build the truck, they know that Toyotas sell on the reputation of unparalleled reliability. To ensure that these are still on the road in 20 years rather than the scrapyard, Toyota spends their money on more robust components and less of their money on things that aren't as value added to your midsize, BOF SUV buyer. Maybe Toyota's internal testing showed little fuel economy improvement but was an absolute wildcard in the reliability game. Would you say that the 5AT was a bad call given that data and the customer's expectation of reliability?
5) the development of the 4Runner is very sensitive. Yes, they could offer the 5.7L and 6AT. They may also only have capacity for 45k 4Runners to the US each year. Adding the V8 to the 4Runner may cost a lot more than they can get payback because of capacity limitations. (Note: the 4Runner has yet to have cash on the hood other than $1000 in certain regions right after pedal gate.) If they spent that money, they get a few more sales, but the 4Runner project is now a loser money wise, the 4Runner dies for the next gen. The GX exists if you need a V8. When it dies, we might see the V8 come back to the 4Runner, but right now, it doesn't make sense to spend loads of money to develop something only 10% of buyers are demanding. If 4Runner production moved to the US with Tundra and Tacoma, the chicken tax would fall off, cost to manufacture goes way down, and they could afford to offer more things. I'm sure that would piss off the "Japan only Toyota" folks, though.