yesterday my friend broke my sliding glass on the back window. Do i have to replace the whole thing or can i just replace the one sliding piece?

 

I've never had luck with that. Luckily the junkyards around here only charge $35 for a good used one. Your luck may vary. They fit from 80-96 trucks.
Pretty easy to replace yourself. I use a butter knife and Windex. Other folks wrap a string around the weatherstrip and "pull" the new back window in. Either way only takes a few minutes, even quicker with a helper.

 

Since its flat glass, any safety glass place (hint - places that do glass table tops) can cut glass to fit with no problem, and you can put it in yourself. Some sliders require removal of the rubber weather stripping to get it apart, others you can unscrew the tracks, take the sliders out, then unscrew the sliding window parts and put the glass in with the rubber border. Its really a matter of looking at it closely, then dismantling carefully. Watch out for remaining shards of glass, they do hurt, and I find it much easier and safer to replace the glass while the entire back window is laid across a workbench, the garage floor, or sawhorses. Kneeling on your back seat (crew or ext cab) or across the center console (reg cab) is real uncomfortable to say the least.

Hope that helps.

Someone said they found junkyard slider windows for $35, thats an excellent option, as you just remove the weatherstripping, put the new window in, put the stripping back. I need to find a junkyard like that Around here they either want too much, or its rusty, broken, or the weather stripping is shot. I have a solid window and would love a slider, obviously.