I've played around with a couple of different jack points to see what works best with my 4 (3-ton) jack stands and my 3-ton floor jack. As you know, jacking from under the suspension is ideal so you don't have to compensate for suspension droop. So in the rear, I jack up the axle (with a rubber pad) just to the inside of the spring mount points, and then throw a jack stand under the axle as close to the tire as possible. I do it again for the other side as well. I know people jack directly under the rear differential to lift both ends at once, but I've always been leery of that from a structural point of view. I don't know how well all those axle segments are connected (probably plenty well), and I don't want to mess with anything as well-aligned as an axle. This may just be me being way too timid, but that's just who I am.
The front is trickier with the independent front suspension. For that, I've taken to jacking at the center of the main front cross member (the biggest one), and then placing two jack stands on either side of the floor jack, as far outward as possible wile assuring good contact with that cross member. Then I lower it down and slip the floor jack out between them. I'm much more comfortable jacking that single beefy front cross-member, since it's a single monolithic piece of steel.
I'm still not happy with my solution for the front as I do have to overcome the suspension droop, but I'm pretty happy with the rear jack points. Also, no blocks of wood necessary. I may still buy myself a floor jack extension however, just so I'm not squeezing the floor jack near the end of its range.
Also, I can attest that jacking anywhere along the main frame is just fine from the truck's point of view. Those frame rails are super strong. The poor little 3-ton jack stands might protest, but each one of them "should" be able to lift the whole darn truck by itself. So, whatevs, suck it up jack stand.