I have had the fronts replace a couple of times in the past, and now recently, the rear, upper and lower. However be advised that if you put it off, it has an effect on the control arms in the rear. I had to have the lower rear control arms replace, as they had worn so badly that the new bushings would just fall through the end, and the extended warranty would not replace because there was evidence of corrosion. That cost an extrat $250 to me. the extended warranty covered the bushings and the labor to install the new control arms. I would not recommend putting it off, as you will probably end up in the same boat.
Changing the rears changed a lot, as the front was wandering a little bit, and now the whole truck feels tight, even though just the rears were replaced.
Funny though, the next day I went offroad with a dealer event just for grins, and near the end heard a lot noise every time the front end hit something. The dealer mechanic looked under the front and found the left front bushing had actually cracked all around, so it is back to the dealer this week.
My advise is not to put off bushings, as they have so much to do with how your truck handles, both on and off road.