I've got an '06 Cummins 2500 4x4 G56 with a SBC 3600 DD (SFI approved lever pressure plate and 12 pucks per disc).

I had noticed that the transmission was getting harder to shift and that there was an unpredictable clunking noise. The noise only happened when the transmission was in neutral with the pedal out. Sometimes it would cause a vibration in the floor board. Once again the clunk was unpredictable as to when it would happen and it sounded like it was coming from the front of the transmission. I also have the problem of where the transmission is sometimes impossible to get into second gear when at a stop light.

I removed the transmission and clutch this weekend. There's some unusual wear on the pressure plate and floater plate, but I don't wish to discuss that yet as I haven't talked to SBC yet.

I went ahead and started to disassemble the transmission. One of the first things that I noticed is that the conical roller bearings on the main and countershafts have some wear. The wear is on the individual rollers. I'd imagine that the races also show wear, but I didn't have time to look. The tranmission has 69k miles and has about 35k miles with the SBC clutch. I also installed Amsoil ATF when I installed the DD.

My question is whether the wear on the rollers is usual. My first thought is that it is not, but I am not a bearing guru. Any useful thought , comments or insight is appreciated.