The earlier (GM) 6.2s were a bit problematic and not very convincing as the other guys touched on. One big problem was the glow plugs swelling in the heads. (Which was quite common.) They didn't last long in the first place, and if they swelled and you broke one taking them out, off with your head. NOT A CHEAP OR SIMPLE JOB. They also weren't too brag-worthy on the power side either. All around common comute to-and-from-work/store engines in my book. If you put an injector pump in, you might as well change the injectors too. Whatever wore away from the inside of that pump is probably sitting in the nozzles of the injectors. (restricting the spray pattern) Also, a pump installed is gonna start around $1,200.00. AND it HAS to be timed. (The 6.2 was pre electronic control) I don't know of any shops/parts stores that rent diesel injection pump timing equipment (Time-Trak etc..) and it is very expensive to buy if you're only gonna use it once. One member mentioned the 7.3L. It was a good motor for it's day. It is actually an International (Diesel) motor, and too was pre-electronic control. The biggest problems I saw with those were the lift/transfer pump check valve, (Trivial) and injector pump shut-down solenoids. (Also trivial). There were glow plug concerns, but most of that was tied to the controller or short lifespan of the plugs themselves. (Never had one swell in the head.) The successor of the 7.3 was jointly developed by Ford and International. It was the T444E. (Tripple 4 E) It was actually the same 7.3L, (7.3L is actually 444 cu in) but was electronically controlled with HEUI injectors. It was a good motor and there weren't any real issues with it. Inectors and glow plugs at about 150k miles comes to mind. And IPR (Injection Pressure Regulator) failure. Not too bad. Also The oil gally plug seals prematurely failed, but were upgraded. Enough on that. One member mentioned a good gasser for what you want. He/she is pretty close in that suggestion. Diesels are designed to work/run. If you are just towing around a 6x6, it may be a bit of over-kill. I have a 4.3L gasser in my S15 Jimmy and I tow my 1969 19ft cathedral hull fiberglass all over without a big concern of gas mileage or power. In fact, this motor/drivetrain is advertised to pull/tow 5000lb. It does OK. Also remember, that even with todays hi-tech electronec controlled diesel engines, the worst thing for them is to let them idle. And if you do alot of city driving, it's a waste in my book. As I said, they are designed to work/run. This was supposed to be my 2 cents worth, but now that I read it, it's more like a-buck-and-a-half. Sorry for being so winded, but if it helps. GREAT. I don't want to talk you out of anything, just weigh your options.
It's all just nuts and bolts.