Mitsubishi bd2g clutch problem.

I have a Mitsubishi bd2g dozer that while running for a moment would eventually stop pulling. I pulled the floor plate off and noticed that it would pull fine for a second and then gradually the drive shaft below my feet which stopped turning but the motor would continue running which made me think that the clutch was slipping. The gentleman who owned the machine before me and just had a collection pressure plate put in it less than a year ago. Also noticed when I was pulling the transmission out of the dozer that I saw a lot of trash and one of the filters in the bottom part was stopped completely up. I tore it down put it back together after cleaning that filter thinking that perhaps the sump filter being stopped up might have caused my problem. After I have a reassembled it I can still turn the primary shaft that goes into the clutch plate by hand when the clutch pedal is not pushed in. I'm not familiar with wet clutches and didn't know if this perhaps had anything to do with it or if I need to take it back down and inspect the pressure plate and clutch plate