98 will not move

[Erik the Awful]

Check your fluid level with the engine running. If you have fluid and it doesn't move you need transmission rebuild. It could possibly be a torque converter issue, but usually there's noise associated with that.

 

[Schurkey]

Shift linkage INSIDE the trans has disconnected? I had that happen on a Powerglide, about a thousand years ago.

Plugged trans filter, pump can't pull fluid? Had no reverse when cold on my Trailblazer 4L60E, fixed with a fluid 'n' filter change.

Drop the pan, look inside.