For your transmission question, any extra stress on the tranny gonna shorten its life, definately. But it's not your mods that will cause a premature death, it's how you drive it. You can be an idiot and stress the crap outta your tranny, or you can drive wisely, take care of it, and you'll get a lot of extra life out of it (gotta have a little fun, though). Dexron VI tranny fluid is excellent, only use a GM filter, get a good shift kit, and don't have it flushed, it's safer that way unless the person knows what they're doing and they probably won't.
Do some research on how our tranny's work, seek to understand what makes them tick, and then you'll know how to prolong its life. There's a ton of info on here for you to digest.
