Well, the extraneous body/interior components have always been Chrysler's weak point, haven't they (well, at least, in the last...45 years or so).
Their transmissions sucked for a long time (well, after the Torqueflite 727), and their engines were mostly completely gutless for a long time, as well. Now they've seemingly fixed those issues.
I think if you went with the Durango, my bet would be that you'd probably get pretty good service out of it. It's a big, heavy truck with a powerful engine, so, you'd probably have some driveline parts wear out if you planned on keeping it out of warranty, so, I'd just count on that from the get-go. More so if you'll be driving it in town a lot; less-so if it will get mostly highway use. Also, from what I've seen, Chevy and Chrysler, especially, tend to use some cheaper parts as far as alternators, starters, water pumps, fuel pumps, etc., as compared with Japanese vehicles.
The 4Runner will be easily rock-solid reliable for 300,000 miles at least. You're not really going to have to worry about any of the [censored] I mentioned above. And it looks a helluva lot better than the Durango. Actually, personally, I think the Jeep Grand Cherokee looks a lot better than the Durango.
4Runner a slug? Not real sure where you're getting that idea. It has the latest iteration of the 1GR-FE 4.0L DOHC V6 with dual VVT-i. Wiki says it's rated at 285 HP/289 LB/FT TQ. on 91-octane fuel. Car & Driver says 0-60 mph in 7.5 seconds. I wouldn't call that a slug. That was Mustang GT territory up until the mid-90s.
Sure, the tranny only has 5 speeds, but it's bulletproof behind that engine. I have that same transmission (Aisin-Warner A750E) in my Tacoma (along with the single-VVT-i version of the 1GR-FE). It's been used with V8s in other applications (4Runner when they offered the 4.7 V8, Sequoia when it had the 4.7 V8, Tundra, etc.), so, it's understressed motivating a V6 4Runner.
That 8-speed in the Durango? I understand it's being used by a lot of different OEMs, but it still doesn't have a real track record yet.
Anyway, no real doubt in my mind at all that if you're looking for a vehicle to keep for a long time, well beyond warranty, you're going to spend a lot less money and time on maintenance on a 4Runner, than a Durango.