Oh, I agree to take it to a shop if you don't have the tools/skills. I wouldn't tackle that without a good lift and some help. Those things are heavy. I also agree it depends on funding and how much peace of mind you want. Junkyard trannies are cheap but no guarantee how long they can last. They may last 10 more miles, or 100,000 more miles. A quality rebuild of your current tranny or purchasing a performance tranny may be well worth it.
Darrin at BCAutomotive is fantastic when it comes to rebuilt and performance 4R70W applications. A few customers I know paid the same price for these built up transmissions as they would have for a rebuild of their current transmissions with lower quality parts.
http://www.bcatransmissions.com/index.html
Don't let the site fool you, he's a very good guy and knows what he is doing. your local shop can install a shipped transmission just the same as any other.