Buddy had a late 80s 6.9 IDI. It refused to die. He towed a monster 5th wheel with it and it finally rusted away to nothing with about 550k on it. He only ever did basic maintenance and maybe a glow plug relay. It got pretty good mpg for a dually (over 20), but it was pathetically slow. Embarassingly slow. It actually had the torque available to keep the 5th wheel moving, but just awful
The 7.3 IDI was the same critter, just more displacement. Still slow
7.3L Powerstroke started in late 1994, often referred to as a 94.5. It continued through the OBS without an intercooler (but the aftermarket has you covered.... although it doesn't really help unless you're turning up the power. Starting with the 01 they all came with an intercooler (except vans).
Unless you find a really flawless example of an IDI, they are all 30 years old now and will likely be rotted, wasted, or otherwise crushed. Even if you find that unicorn, be prepared for (see: embarrasingly slow comment above). The 7.3L Powerstroke is way better, but they come with the tax. It seems like anyone buying a PS is instantly willing to pay a base rate of $10,000 just for the pleasure of owning it. If you find one, you'll find that they tend to be wonderful. For the most part any gremlins they have are all super easy fixes. Glow plug relays like to die every 60-100k. Cam position sensors can take a hike around 150-250k but they're a 10 minute swap. The wiring for the glow plugs is molded into the valve cover gasket and they can fail causing some glow plugs to not work.
I've owned a few 7.3L strokes and I absolutely adored them. Great mileage, awesome torque, super reliable, but I stopped giving up hope of ever having one again. Old wasted PS trucks selling for crack money these days.