Can I make my back windows power windows if there push out windows on my 2000 Chevy Silverado 1500 crew can

You can try and pick up regulator/motor at a salvage yard, the real challenge is adding the circuitry and power. Your factory harness will not have support to add on accessories, so you'll have to run your own circuit. It will not be a part of the anti-theft system either. Here's a tip: a typical salvage yard does not separate doors - if you want just the motor, you'll end up buying the entire door. But places like "pick-a-parts" or "pull-a-parts" will sell any bit or piece. Problem is with those places is selection can be fairly limited or well picked over. Converting manual windows is not cheap nor is it easy. It's not the mechanicals that makes it hard, it's the electronic/wiring part of it.