Slow as the day is long, don't take well to power upgrades, but are a good reliable unit with pretty minimal maintenance requirements.
My old man's 2001 7.3 With just the Edge Products Juice Attitude kit, intake, and custom turbo back exhaust towed 5th wheels and could scoot just fine all with manageable EGTs. Certainly not a race truck by any means, and no doubt there are better platforms if thats the goal, but popping it into power level 5 on the fly would give it enough pickup and go to overtake 75% of vehicles you would encounter on a day to day basis (at least until that darn speed limiter comes into play lol)
In stock mode it leaves a lot to be desired, and when the engine is cold, forget about pulling into traffic in a hurry haha
The trans is a potential weak spot. My father's has well over 200k and the only thing he has had replaced was a billet input shaft installed, and had the trans rebuilt at the same time, and that's about all its ever needed other than brakes and ball joints.
Its been a reliable truck for him, and seen its fair share of heavy hauling. I would not hesitate to buy one.