A 3x3 chunk radius is constantly loaded around the player with the player obviously always in the center chunk. Going from Door A to Door B is no problem at all because the chunks are already loaded. Going from Door 1 to Door 2 seems to be impossible. I've tried making Door 1 load up Door 2's chunk before you walk through it and, while it works, does not work going back the other way. Every method I've tried at best works in only 1 direction or at worst sends me into the void. Real head scratcher...