Trans. slipping?

'99 Durango transmission does not shift between 2nd/3rd correctly. Kinda sticks in the middle and spins without adding speed. After a few seconds it shifts and goes on with business. Does not do it all the time...seems to happen more when cold and/or being easy on the gas. Any ideas? Please advise.

Have you changed tranny fluid?

That was my first thought...changed but did not help. Other said it was a "front band" that was worn. Broke down and scheduled to have rebuilt. Thanks for the help.