I agree it sounds like the Sun Shell either stripped the splines or it broke.
Its a common failure on them.

So what would be the best thing to do....get the sun shell fixed or get another transmission

An old coworker of mine had the sun shell replaced in his '98 Bravada for something like $450 a few years ago. He's still driving the truck. So it can be done. If your trans was shifting fine before, you likely have a good candidate for just replacing the sunshell. A good shop will let you know whether or not they think the clutches/bands look good once they open it up.

You would probably pay more to have a used transmission put in and could end up in the same boat again.

Ok thanks....I really can't wait to get back home and drive my truck....I love it.....