started up my 2000 jimmy 4x4 4.3 got in and put in reverse and it started moving. i got to the shop door at work and needed to give it a little gas to get up over a 3 or 4 inch lip and i heard a clunk and now all it will do is rev. i put it i drive 1 2 and it moves fine. any help or ideas?

 

Do you have a check engine light? Does it shift normally other than no reverse? Sounds to me like you may have broken the sun gear shell.
I hate to say it but you will probably have to get it to a trusted transmission shop for further analysis.

 

no lights everything else seems good

 

So you have no reverse but it shifts completely normal otherwise? How much have you driven it since this has happened? I believe you will start to notice other problems the more you drive it.
I guess just be careful not to park so that you have to back out...lol

 

Reaction Sun Shell. I bet you tore the splines out of it. I bet you will find that you no longer have 2nd or 4th gear as well.

 

Reaction Sun Shell... that's the words I was thinking of...
Yea, seems to me that tranny has gotta be showin more symptoms than mentioned.

 

1 and 3 thats all. 1200.00 for just the sun gear 2500.00 to rebuild everything