What do you think is wrong ?

I have a 1998 jcb 214s ll backhoe with a power shift transmission it overheats fast and the transmission locks up in two gears at once you have to shut it off let it cool off then it will run for a little bit again I put new clutches in it but it is still the same I have heard the plastic pistons may have swelled and need to be changed to the metal ones any body else have a problem with this.