All of the above....
I think I'm going to add a locking diff this spring. Kinda spensive tho., but cheaper than a new vehicle.
I go to all sorts of diff ramps all over and i have a 2wd dodge ram. I found that new tires help a little, the rubber has not gotten hard yet, and if all of the above and newer tires dont help, you can always use the ghetto bounce method in extreme cases. Get your buds in the back or on the bumper, have them jump up and down and give it a little gas on the "down strokes", use the boat to help push too. Works.
Also very entertaining for the on lookers as well.