Regular maintenance and replacement items for a 140k+ mile vehicle notwithstanding, it's quite solid. The AMC 360 V8 still holds 40 pounds of oil pressure hot, the bulletproof Chrysler 727 tranny shifts like a charm, and the NP229 transfer case works flawlessly.
The two main sources of problems with the truck crop up when the Ford-sourced parts, the carb and ignition, decide to go south. The stock Motorcraft 2150 carb can be temperamental to tune, and has a mixed reputation for reliability. A small backfire usually will kill the power valve, requiring a minor, but still inconvenient replacement. Its layout is a tad complex (not unlike most carbs, though), and the linkages (choke, accelerator pump, etc.) need to be kept adjusted and lubed to avoid problems. As carbs go, I've found it to be mediocre at best, as compared to other comparably-sized units, such as the Holley 2300. At 125k, I replaced the worn stock 2150 with a re-manufactured unit, and will probably be switching to GM throttle body injection by the end of the spring, in the hopes of pulling more efficiency out of the induction setup. The key is getting it setup and tuned correctly; if you can do that, and keep it that way, you'll be set (it can be done).
The Ford Duraspark ignition works well, provided that the ignition control module doesn't go bad. The distributor is a solid design, but the module is the weak link. The stock unit went 115k, but aftermarket replacements I've found only last about 5-7k tops. Their failure is marked by sporadic stalling, and usually occurs at higher engine temperatures. Keeping a spare ziptied to the mounted one is good insurance against being stranded. Should one fail, you just switch two connectors, and you're on the road again.
Other than that, most everything else I've replaced was just a function of normal wear, rather than poor design or build quality. (The one exception being the poor clearcoat metallic paint, which was common most all Jeep and Chrysler products of the era.)
The alternator has been replaced, after the stock unit went for 113k.
The radiator was replaced after a seam wore out after 124k of service.
The steering gear has developed a little bit of play, and a slight seal leak, and is due for replacement, but it's in line after almost 150k.
The fuel gauge sender unit works, but is afflicted by the typical resistor deterioration woes inherent in the ancient AMC design, and can read a little low below a half tank. It's easily remedied though, with a $40 replacement. Thankfully, the tank access plate in the rear floor makes replacement possible without dropping the tank.
Other than that, two or three minor electrical glitches spawning from either component wear, age, or mild corrosion have been easily fixed with little cost or effort. The rear window can be temperamental, but works well after being serviced properly.
This Jeep is simply the finest vehicle I've ever owned. It's got ample power, plush comfort, unmistakable styling, and is extremely accessible to work on.
I have found nothing that handles better in snow, and the 360 makes highway driving fun (even though fuel stops come up around every 200 miles).
Those who see past the typical gremlins that can come with older cars make up quite the cult following for these trucks, with a camaraderie among enthusiasts.
It can hold its own against any other of the more modern vehicles in its class (that have the advantage of 30 years of technology) that are currently rolling of the line, and has the added benefit of not costing $30k.
Its styling is nostalgic, complete with vinyl woodgrain trim and plenty of chrome. Finding it in parking areas is never much of a challenge. Also, the wide expanses of glass and slim pillars make for unrivaled visibility. Cargo room is exceptional, and the seats are quite comfortable even on the longest trips.
My only complaint with the truck is its lackluster gas mileage, which typically averages about 10mpg/city and 12mpg/highway when properly tuned. It's understandable, though, considering the classically square body design, and its primitive engine control system. Seeing as MPFI and mildly improved aerodynamics net current fullsize SUVs 15mpg on average, the GW isn't really all that thirsty.
Regular maintenance is essential. Keeping the sheet metal clean will stave off the potentially serious rust that plagues some older Jeeps. The AMC V8s oiling system benefits from regular oil changes, especially at higher mileage. If you keep up with it, 150-200k is not unusual for the high-nickel 360s.
It's important to remember that most of the issues that arise with these trucks are due simply to the fact that they are now at least a minimum of ten years old now, and many have more than 100k on the odometer. The design is inherently solid, and time-tested, as the platform's 30-year run went by without any major changes to the original 1962 design, but they do occasionally require component replacement when parts wear out, as would any vehicle of the same vintage would.
For the most part, the truck is quite accessible to work on, with many parts readily available. The fullsize Jeep line shares enough componentry with both the popular Jeep CJ line and other Big-3 products so that replacement parts coverage is quite good. The truck's older design and convoluted vacuum line system can make finding the right mechanic difficult, as many do not understand the quirks found in older Jeeps, and are unfamiliar with older technologies. So, knowing a little about the truck can be helpful. Quite a few enthusiast groups, such as IFSJA (www.ifsja.org), exist for Fullsize Jeep owners, and are the best sources for solving problems or answering questions without consulting an expensive and potentially unknowledgable mechanic.
I guess that in the end, if you want a truck you never have to tinker with, and can just drop off at the dealer when a problem crops up, you want something new with a warranty. But if you don't mind saving $25,000 and learning a little about the quirks that can come up, and then tackling them, the Grand Wagoneer is affordable, attractive, capable, comfortable, reliable, and an all around blast to drive. Nothing currently out on the market can compare.