Nice! That's the exact truck that I have. And you got it for a darn good price -- I've seen them go for up to $5,000 or so.
Yup 84HP stock. I've pulled a 2,000 lb trailer with mine -- that makes it pretty slow on the hills, but i could keep up 60 to 65 on the flats. It's faster than my subaru wagon, which is also 84 horsepower, and probably 1,000lbs lighter (and only 100 ft lbs torque instead of 140) I was always going to add an intercooler to mine sometime, but haven't gotten around to it yet. Putting a boost controller instead of the wastegate might help too, from what some friends with mercedes diesels have said. I get between 10 and 12lbs maximum boost on mine.
I had a valve rocker arm go out on mine last fall -- then I drove it on 3 cylinders for another 60 miles till it broke another 3 rocker arms (had no choice, a giant snowstorm was coming and I had to get home). I put new rocker arms and rocker arm shaft in it, and it's all better now. Not sure exactly why the first one broke, but perhaps from letting the valve clearances get misadjusted. The mitsubishi dealer here had the new parts, and rockauto.com has some stuff for it too. Only other problem I've had was the exhaust manifold keeps coming loose -- I've bolted it back on three or four times now, but the nuts keep coming loose, then you lose turbo pressure because the exhaust is escaping before the turbo.
I am running 205/75R15 studded snow tires on mine, and had 215/75R15 all season tires on it in the summer. It looks like you could go a bit larger diameter, but the front wheels will start rubbing if you go to a really wide tire (I have a dead '82 gas 4x4 mighty max with 10" wide tires, and they rub on the rear of the fenders). I've taken mine off-roading a little -- jeep trails and such, and it does suprisingly well. Not great departure angle, or as much clearance as a stock toyota, but great torque and throttle response.
As far as mileage, I've gotten between 22mpg and 26mpg on mine. Averages around 24. The previous owner used to get closer to 27 regularly, but he didn't have the topper on it, or the toolboxes in the back. I figure with the weight I've got on it, and the roof rack hurting my aerodynamics, and doing alot of mountain driving, 24 isn't bad -- friends with similarly equipped toyota gasoline trucks are getting 18 or 19. I am also running biodiesel most the time, which gets you slighly less mileage than diesel (but it idles so much smoother, and doesn't put out black smoke like it does with diesel).
Make sure you let it cool down before shutting it down -- it's an oil cooled turbo on this, so you'll cook the bearings if you shut it down hot. I've always run synthetic oil since I've owned it.