The 6.2L is a Detroit diesel. It was slow as balls (around 150hp, 250ft-lbs tq), but being all mechanical and non-turbo it would be easy as pie to fix if something ever goes wrong. 180k isn't that bad of mileage either.
There are a few things to watch out for according to Diesel power:
•Coolant leaks: Caused by external hoses and head-gasket failure, especially on '88-'96 trucks.
•Oil leaks: Oil pan design and early rear main seal are likely problems.
•Hard starting: Glow plugs prone to failure due to malfunctioning glow-plug controller. High compression ratios and the starter solenoid design only added to the problem.
•Excessive engine vibration: Due to harmonic balancer separating, which leads to crankshaft failure.
•Cylinder-head cracking: Due to overheating or poor casting quality.
•Engine-block failure: Due to insufficient casting quality, '00-and-later blocks are best.
•Electronic-injection-pump failure: Caused by overheated pump-mounted driver (PMD) and not a failed injection pump.
Don't let that scare you though. You're basically looking for the things you would normally look for when buying a diesel. Make sure there isn't any water in the oil, nothing is leaking (though Detroits always leak a little

), the block isn't noticable cracked, and it starts/runs fine.
As long as you don't see any of those things it should be good. Those engines are designed to last 300,000 before a rebuild is recommended. If you get it I could go over some maintenance stuff with you that will keep it running fine. If it had a manual tranmission it would be pretty bullet proof, but since it has a slushbox I'll talk about that too:
The 4L80E is the same trans I have in the '95 suburban. It's basically a computerized 700R4 (which is a turbo 400 with an overdrive). Generally they are pretty good (though not as good as a Turbo 400). The shifts are controlled by computer so it could be a problem with the electronics. The problem could be something as simple as a blown fuse. That would put it in limp mode (locks out first/third/overdrive) and you would just have to disconnect the batterys and reconnect them after changing the fuse. Next it would be the sensors (Imput/Output/Fuel pump TPS). If it is a bad seal you can buy a seal kit for less than $100, or a more complete seals, gaskets, bushings, clutches, steels, ect kit for ~$300. Chances are that will take care of any problem it has. Even if you need a whole new trans you can find them with low miles from a junkyard for ~$500.
Now, even though I'm a diesel guy, the 5.0L would also be a good truck. It has a bit more power (185hp/275), and is based off the 350, so it should be pretty reliable. You know the history of it as well, which is always a plus. However, it will use more fuel than the diesel, so you have to figure out what the costs to run each would be.
I would say they are basically pretty comparable and it would come down to which you like more (or drove better, but since you can't drive either that's mute

). How many miles are on the gasser?