more capable offroad then an American vehicle? well thats a first ive ever heard that lol! I still have yet to get stuck in my Suburban, and ive been in some pretty rough stuff in that. Around these parts, where we have a lot of mud in the summer, and need to drive in the fields, and during the winter have blizzard after blizzard, you need a good, strong, hefty vehicle to handle it all, and American trucks and SUVs are everywhere, with anything imported usually being towed out. Maybe as far as size is concerned I could see it being a bit of an issue if your wheeling a small trail, but otherwise, they are awesome off road.
Yes the 4.8L and 5.3L are very very similar, and like you said, they do share a lot of the same parts. I actually have a car craft magazine where the boys bought a silverado 5.3L and were gunna see how much power they could bolt on it before it broke, with no strengthining of anything really. they got well past 600 HP and it was still asking for more, when they looked at a casting number on the block and realized it was actually a 4.8L, so these engines are very stout indeed.
As far as being smooth/refined and mordern, with the 5.3L, you get that, and you dont have a whole hellofalot to worry about. Reliability on these as ive illistrated before is well above average. Great engines. Cant go wrong. But I would advise not looking at a 2000 Tahoe, and instead look for an 01-04 one. not only was the engine majorly refined in 01, they also went with a new transmission too, which is worlds ahead of the old one. the first year (01) did have some problems in that tranny with the butterfly gears, but that issue has been addressed in recalls and just people breaking down and getting new transmissions afterward. My dads 01 Tahoe had it, went out at 37k miles, got a new one, now the truck has 230k on it with no issues.
otherwise, all of those options you layed out, well, you wont be disappointed unless you buy the Nissan haha.