When I removed side windows last, I slid the front one to the rear and used a wide cold chisel to start the rubber weatherstripping to the 'out of the truck' position. I worked carefully until I had most of the gasket off and pulled gently. I think it'll be easier to replace the entire unit rather than one individual window. To replace it in the other truck, you'll need someone to hold the window unit along the outside rail, use some heavy string or twine wrapped around the rubber gasket, liberally coat the rubber with 409 or similar soap, then pull the string from the inside to get the gasket over the rail. All should be well after that.

It may take more than once, but this should be about 1 hour overall for removal and replacement.