Going to Roswell for a second opinion, or Sloan-Kettering in NYC certainly sounds like a very good idea. Like you, I would not be happy to be told to wait three months for another CAT scan. I think you are wise to be assertive in this case.
And your colonoscopy advice is good, too. The procedure itself is not bad at all and the prep isn't as awful as it used to be. Colon cancer is one of the very few cancers that can be prevented with screening.
I'll be thinking of you and your Dad, Phillip, and holding you in my thoughts.
Leslie