3.0 shifted into reverse, heard clunk, and really weak rev now
 

So,
I put my truck (99 Ranger 3.0 4x4 Flexfuel, not sure what tranny) in reverse and heard a thunk. After that, I have hardly any reverse, but I can feel it is trying slightly to move.

My questions are:

Will I hurt the Tranny any more if a drive it? If so, how long do I have?
Is it a band or module/solenoid?
Will a computer give me a code or tell me where to start?
How do I figure out my Tranny model?

Thanks for the Help,
Ford for Life!