I have a 2000 ls 3.9 I bought a few years back with 100k miles. I've done timing chain tensioners (uppers only) that I thought was a rod knock or spun bearing but an easy fix, water pump, brakes, coil packs, alternator a real bitch, valve cover gaskets, clockspring, tierods, bushings, ball joints, torque rods, hubs and bearings, fuel pumps, dccv which still didn't fix it lol, and some other things. The only thing I had a shop do was rebuild the trans and I was told by a computer whiz at a local speed shop the manual trans from the 6 cyl can be made to work in the 3.9 but I can't be sure.
She now has 207k miles and doesn't burn a drop of oil or leak any, always synthetic. If you can do the work yourself these are really good and well balanced cars that will last if you take care of them.