KM c6500 Jam... Timing issue?

[ITHPP]

Hi there,
I am not much of a tech but I need help. I have a KM Bizhub Pro c6500 that continues to jam as it goes into the duplex unit. Pretty consistently will print about 7 sheets...then jam. I have a parts machine that I have tried many parts off of, replacing the clutchs, the rollers, the drive motors, and even swapping out the entire ADU drawer. I have checked the solenoids in I/O mode and all work fine. I have check the individual paper drive motors and they work fine too. The paper gate on the duplex unit sounds like it opens on cue. I have cleaned off all photo sensors, cleaned up all the rollers, checked thoroughly for any signs of damage or random paper pieces perhaps caught in the machine. But it still jams at the same place after the same amount of prints. I have tried 20# paper, 24#, 28# and it still always jams the same time and place. The paper jams and packs up at the M9 gate every time.
After changing out the entire ADU it was completely the same so I wonder if there is an internal timing/code issue? I know these machines are pretty common and have been around for a long time now. So...does anyone have any thoughts of what the problem might be? I have searched the forums and jamming on the C6500 seems common....but I just can't find the solution yet.
Is there a way to check and re-calibrate the timing for the whole machine?
Any thoughts would be very helpful.

[K-3]

jam code and did you try a different fuser

[blackcat4866]

I think a jam code would help lot. =^..^=