So what does ford need to jump ahead (of the Tahoe)?
More horsepower? More torque? Better gas mileage? Higher towing capacity? Nicer interiors?
They will not jump ahead any time soon. Tahoe, Suburban, their GMC/Caddy brothers, Sequoia, QX, GL class all ride well enough that if you spend 12 hours in them, you don't feel beat up at the end of your drive. Ford needs to improve their ride.
Ford I believe is class leading in power so that doesn't even need to be brought up. It's how they develop that power and the longevity a boosted engine really has.
The interiors are purely preference. Some people rave about Sync and my touch. Others hate it. I think Chevy needs to improve too. MB GLs and Infinity QX handily beat Chevy and Ford. But that's a Navigator/Escalade comparo.
The mileage is fine. If you buy a full size SUV and your primary concern is fuel economy, why are you buying a modern land barge? This is probably why I'd make a terrible sales person. Fuel economy should be an after the fact bragging right in full size BOF SUVs.
The Ford's are fine. But the reason they won't pass the Tahoe is because Ford makes a product and sticks with it far too long. There have only been 4 changes to Mustang in the last 45 years. 4 to F-150 in 40 years. I could go on but you get my point. They are rarely class leading in anything because they don't innovate. Thanks for the moving assembly line. Every other time Ford tries to innovate, its usually a fail. Ecoboost is a sucess for now. But to beat your competition, you have to do everything it does better. For Tahoe, that's 250,000 miles of comfortable, relatively trouble free driving with enough features to keep a driver loving their car a little more every day. The ink isn't dry on the first sold 2018 Expeditions so it's hard to say if they will be preferred over Tahoe, but I doubt it. I think they aimed to be relevant again. There is nothing new or exciting about this new version. You may as well call it a new model instead of a new generation. Lincoln, you could likewise look at as a new upstart car company because they are doing everything completely different as evident in the Navigator and Contentential.
Maybe you prefer the Expedition. It looks nice. But then again, so does Tahoe, QX, Sequoia... It handles well thanks to a modern setup. So does Tahoe, QX... does it ride well? I don't know. Haven't driven one. Bit if Ford's past SUVs are in this new Expedition, then no. Did they fix the glitchy Sync system? Don't know. We'll find out in about a year.
What do they need to do to beat the Tahoe? It doesn't matter at the moment. They need to first make a vehicle that is worth a damn in its own segment. And on that point, so does the Nissan Armada. Then they can start fine tuning it to beat Tahoe.