1993 Ford Explorer making noise

I noticed that when I start to take off from a stop or when going up a incline the vehicle starts to make a noise fron the transmission and it dosent want to go. If you accelerate slowly it seems to be ok but more often than not it makes that noise. I was told by the transmission shop that the clutches in the transmission were shot and that it would need to be rebuilt at the tune of $1100.00. Is this a problem I may be able to correct myself by changing the fluid and servicing the tranny or is this going to be a costly repair. I had the tranny replaced once already in 2003 and just cant figure out why it would need it again allready.