Approaches to launching new products in existing businesses?

What's your experience launching new products in established businesses?

I've tried this twice in two different companies. It starts out great. The intention is to treat it as a separate team with its own tools and process, but it never works out. You end up using the same dev tools, marketing, and sales process. You get bogged down by the primary business, and ultimately fail to innovate. In one experience I had, just getting a website up to validate the idea with prospects took months..

What is your experience? Any hacks to increase the success rate?