Not sure you really want to take that off at all..... Think you would have to drop the pan, but, not 100% on that. (everything I know about auto transmissions is written on the inside of my left eyelid.)
If you don't have it already, grab one of the service manuals from the faq section here. Procedures for removing the various parts are in there. Might help some.
If the t-case doesn't want to separate from the trans..... there really shouldn't be anything holding it on, once all the bolts, linkage, and electrical connections (if any) are removed..... careful how you pry on that though, as the housing is only aluminum.... easily damaged.
Oh, and: Welcome to DF! You should put your truck info in your sig, and profile. Makes life easier for us to help you.